Thermally actuated microvalve device

ABSTRACT

A microvalve having a generally planar plate valve body defining a chamber and a plate valve member movable in the chamber about a pivot axis that is perpendicular to the valve body to control the flow of a fluid through the valve body. The plate valve member defines a pair of opposite faces, a first duct therethrough provides fluid communication between the opposite faces to equalize fluid pressures acting on the opposite faces in the region of the first duct. The plate valve member also has a second duct therethrough that provides fluid communication between the opposite faces to equalize fluid pressures acting on the opposite faces in the region of the second duct. The first duct and the second duct are equidistant from the pivot axis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/533,893, filed Mar. 22, 2000, now U.S. Pat. No. 6,845,962, thedisclosures of which are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

REFERENCE TO A “MICROFICHE APPENDIX”

Not Applicable.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates in general to semiconductor electromechanicaldevices, and in particular to a microvalve device having a pilot valve.

(2) Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 1.98

MEMS (MicroElectroMechanical Systems) is a class of systems that arephysically small, having features with sizes in the micrometer range.These systems have both electrical and mechanical components. The term“micromachining” is commonly understood to mean the production ofthree-dimensional structures and moving parts of MEMS devices. MEMSoriginally used modified integrated circuit (computer chip) fabricationtechniques (such as chemical etching) and materials (such as siliconsemiconductor material) to micromachine these very small mechanicaldevices. Today there are many more micromachining techniques andmaterials available. The temm “microvalve” as used in this applicationmeans a valve having features with sizes in the micrometer range, andthus by definition is at least partially formed by micromachining. Theterm “microvalve device” as used in this application means a device thatincludes a microvalve, and that may include other components. It shouldbe noted that if components other than a microvalve are included in themicrovalve device, these other components may be micromachinedcomponents or standard sized (larger) components.

Various microvalve devices have been proposed for controlling fluid flowwithin a fluid circuit. A typical microvalve device includes adisplaceable member or valve movably supported by a body and operativelycoupled to an actuator for movement between a closed position and afully open position. When placed in the closed position, the valveblocks or closes a first fluid port that is placed in fluidcommunication with a second fluid port, thereby preventing fluid fromflowing between the fluid ports. When the valve moves from the closedposition to the fully open position, fluid is increasingly allowed toflow between the fluid ports.

A typical valve consists of a beam resiliently supported by the body atone end. In operation, the actuator forces the beam to bend about thesupported end of the beam. In order to bend the beam, the actuator mustgenerate a force sufficient to overcome the spring force associated withthe beam. As a general rule, the output force required by the actuatorto bend or displace the beam increases as the displacement requirementof the beam increases.

In addition to generating a force sufficient to overcome the springforce associated with the beam, the actuator must generate a forcecapable of overcoming the fluid flow forces acting on the beam thatoppose the intended displacement of the beam. These fluid flow forcesgenerally increase as the flow rate through the fluid ports increases.

As such, the output force requirement of the actuator and in turn thesize of the actuator and the power required to drive the actuatorgenerally must increase as the displacement requirement of the beamincreases and/or as the flow rate requirement through the fluid portsincreases.

Accordingly, there is a need for a microvalve device capable ofcontrolling relatively large flow rates and/or having a displaceablemember capable of relatively large displacements with a relativelycompact and low powered actuator.

BRIEF SUMMARY OF THE INVENTION

The invention relates to a microvalve device for controlling fluid flowin a fluid circuit. The microvalve device comprises a body having acavity formed therein. The body further has first and second pilot portsplaced in fluid communication with the cavity. The body also has firstand second primary ports placed in fluid communication with the cavity.Each port is adapted for connection with a designated fluid source. In apreferred embodiment, one of the pilot ports and one of the primaryports may be in communication with a common fluid source. A pilot valvesupported by the body is movably disposed in the cavity for opening andclosing the first and second pilot ports. An actuator is operablycoupled to the pilot valve for moving the pilot valve. A microvalve ispositioned by the fluid controlled by the pilot valve. The microvalve isa slider valve having a first end and a second end. The slider valve ismovably disposed in the cavity for movement between a first position anda second position. The first end of the slider valve is in fluidcommunication with the first and second pilot ports when the first andsecond pilot ports are open. The second end of the slider valve is inconstant fluid communication with the first primary port. When movingbetween the first and second positions, the slider valve at leastpartially blocks and unblocks the second primary port for the purpose ofvariably restricting fluid flow between the primary ports.

In operation, the actuator controls the placement of the pilot valve. Inturn, the placement of the pilot valve controls the fluid pressureacting on the first end of the slider valve. The difference between thefluid forces acting on the ends of the slider valve in turn controls theplacement of the slider valve. The placement of the slider valve thencontrols the degree of fluid flow between the primary ports.

The force required to actuate the pilot valve is relatively small.Consequently, the actuator can be relatively compact with relatively lowpower requirements. Furthermore, the displacement of the slider valveand the flow rate between the primary ports can be relatively largebecause the fluid force differential associated with the fluid pressuresof the fluid sources acting on the ends of the slider valve can berelatively large.

Various other objects and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the preferred embodiments, when read in light of theaccompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1A is a top plan view of a first embodiment of a microvalve deviceaccording to this invention partly broken away to show the microvalvedevice in a first position.

FIG. 1B is a view similar to FIG. 1A, except with the microvalve deviceshown in a second position.

FIG. 2 is a sectional view of the microvalve device taken along the line2—2 of FIG. 1A.

FIG. 3 is a sectional view of the microvalve device taken along the line3—3 of FIG. 1A.

FIG. 4 is an enlarged view of a slider valve of the microvalve deviceillustrated in FIGS. 1A and 1B shown in an intermediate position.

FIG. 5A is a top plan view of a second embodiment of a microvalve deviceaccording to this invention partly broken away to show the microvalvedevice in a first position.

FIG. 5B is a view similar to FIG. 5A, except with the microvalve deviceshown in a second position.

FIG. 5C is a partial view of an alternate embodiment of the actuatorillustrated in FIGS. 5A and 5B, showing pressure-reinforcing membersthereof.

FIG. 5D is a partial view of an alternate embodiment of the actuatorillustrated in FIGS. 1A and 1B, showing pressure-reinforcing membersthereof.

FIG. 6 is an enlarged sectional view of the microvalve device takenalong the line 6—6 of FIG. 5A.

FIG. 7 is a perspective view of a third plate of the microvalve deviceillustrated in FIGS. 5A and 5B, showing a bottom surface of the thirdplate.

FIG. 8 is an enlarged view of a slider valve of the microvalve deviceillustrated in FIGS. 5A and 5B shown in an intermediate position.

FIG. 9A is a top plan view of a third embodiment of a microvalve deviceaccording to this invention partly broken away to show the microvalvedevice in a first position.

FIG. 9B is a view similar to FIG. 9A, except with the microvalve deviceshown in a second position.

FIG. 10 is an enlarged view of a slider valve of the microvalve deviceillustrated in FIGS. 9A and 9B shown in the first position.

FIG. 11A is a top plan view of a fourth embodiment of a microvalvedevice according to this invention partly broken away to show themicrovalve device in a first position.

FIG. 11B is a view similar to FIG. 11A, except with the microvalvedevice shown in a second position.

FIG. 12 is an enlarged view of a slider valve of the microvalve deviceillustrated in FIGS. 11A and 11B shown in the first position.

FIG. 13A is a top plan view of a fifth embodiment of a microvalve deviceaccording to this invention partly broken away to show the microvalvedevice in a first position.

FIG. 13B is a view similar to FIG. 13A, except with the microvalvedevice shown in a second position.

FIG. 14 is an enlarged view of a slider valve of the microvalve deviceillustrated in FIGS. 13A and 13B shown in the first position.

FIG. 15A is a schematic diagram of a first embodiment of a vehicularbrake system including a microvalve unit having a normally openmicrovalve device and a normally closed microvalve device according tothis invention shown in a normal operation mode.

FIG. 15B is a schematic diagram similar to FIG. 15A, except showing thevehicular brake system in a dump operation mode.

FIG. 15C is a schematic diagram similar to FIGS. 15A and 15B, exceptshowing the vehicular brake system in a hold operation mode.

FIG. 16A is a schematic diagram of a second embodiment of a vehicularbrake system including the microvalve device illustrated in FIGS. 13Aand 13B configured as a two-position control valve shown in a normaloperation mode.

FIG. 16B is a schematic diagram similar to FIG. 16A, except showing thevehicular brake system in a dump operation mode.

FIG. 17 is a schematic diagram of a third embodiment of a vehicularbrake system including the microvalve device illustrated in FIGS. 13Aand 13B configured as a proportional control valve shown in a normaloperation mode.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of a microvalve device for controlling fluid flow ina fluid circuit is shown generally at 10 in FIG. 1A. The microvalvedevice 10 includes a body indicated generally at 12. The body 12includes first, second and third plates 14, 16 and 18, respectively, asbest shown in FIGS. 2 and 3. The second plate 16 is attached to andbetween the first and third plates 14, 18. Preferably, each plate 14,16, 18 is made of semiconductor material, such as silicon.Alternatively, the plates 14, 16, 18 may be made of any other suitablematerial, such as glass, ceramic, aluminum, or the like. The descriptionregarding the materials of the plates 14, 16, 18 also applies to thealternate embodiments of microvalve devices disclosed below.

It should be understood that the term “fluid source” as used in thisapplication only means a quantity of fluid. The fluid source may be at arelatively “high pressure”, such as the discharge of a running pump, inwhich case fluid will tend to flow from that fluid source to the area ofinterest. Alternatively, the fluid may be of relatively “low pressure”,such as the suction of a running pump, in which case the fluid will tendto flow from the area of interest to the fluid source. The term“non-planar” as used in this application means that the fluid flow,force, or other subject of the term has a significant component actingperpendicular to the parallel planes defined by the plates 14, 16, and18. Other terms which may be used in this application include upper,lower, above, below, up, down and the like. These terms are defined inthis application with respect to an arbitrary frame work in which thedirection perpendicular to the second plate 16 toward the first plate 14is defined as “down” and the direction perpendicular to the second plate16 toward the third plate 18 is defined as “up”. This convention is forease of discussion and is not intended as a limitation to theorientation of the devices described herein in actual use or as alimitation to the claims. The terms “inner” and “outer” are defined withrespect to the relative closeness of the component under discussion tothe longitudinal axis generally defined by the assembly (generally avalve) under discussion, with an inner component being relatively closerto the axis than an outer component.

In this disclosure, reference is sometimes made to a valve being“closed” or a port being “covered or “blocked”. It should be understoodthat these terms mean that flow through the valve or the port is reducedsufficiently that any leakage flow remaining will be relativelyinsignificant in applications in which the microvalve devices describedherein should be employed.

Referring to FIGS. 1A, 1B, and 2, the first plate 14 defines a firstpilot port 20 and a second pilot port 22. The first pilot port 20 isadapted for connection with one of a “low pressure” fluid medium orsource (not shown) and a “high pressure” fluid medium or source (notshown). The second pilot port 22 is adapted for connection with theother of the “low pressure” fluid source and the “high pressure” fluidsource. The first plate 14 also defines a first exhaust port 24 and asecond exhaust port 26. Each exhaust port 24, 26 is adapted forconnection with a common fluid source (not shown).

Referring also to FIG. 3, the first plate 14 further defines a firstprimary port 28 and a second primary port 30. The primary ports 28 and30 are each adapted for connection with a different respective fluidsource (not shown).

Referring again to FIG. 2, the third plate 18 defines a first pilot port20′ opposing the first pilot port 20 and a second pilot port 22′opposing the second pilot port 22. The pilot ports 20′ and 22′ areadapted for connection with the fluid sources associated with the firstand second pilot ports 20 and 22, respectively. The third plate 18 alsodefines a first exhaust port 24′ opposing the first exhaust port 24 anda second exhaust port 26′ opposing the second exhaust port 26. Theexhaust ports 24′, 26′ are adapted for connection with the fluid sourceassociated with the exhaust ports 24 and 26.

Referring again to FIG. 3, the third plate 18 further defines a firstprimary port 28′ opposing the first primary port 28 and a second primaryport 30′ opposing the second primary port 30. The primary ports 28′ and30′ are adapted for connection with the fluid sources associated withthe primary ports 28 and 30, respectively. The purpose of havingopposing ports is discussed below.

Additionally, the third plate 18 includes a pair of electrical contacts32 a and 32 b disposed in corresponding openings formed in the thirdplate 18. The electrical contacts 32 a, 32 b contact the second plate 16and are adapted for connection to a suitable power source (not shown)for providing an electrical current between the contacts 32 a and 32 b.The electrical contacts 32 a, 32 b are illustrated as solder joints, butmay be wire leads or the like. Additionally, it should be appreciatedthat one or both of the electrical contacts 32 a and 32 b may be placedin the first plate 14.

Referring to FIGS. 1A and 1B, the second plate 16 includes the followingmain components: a fixed portion 34; a first microvalve embodied as apilot valve 36 supported by the fixed portion 34 for fully opening andclosing the pilot ports 20, 20′, 22, 22′; an actuator 38 for moving thepilot valve 36; and a second microvalve embodied as a slider valve 40for controlling fluid flow between the first primary ports 28, 28′ andthe second primary ports 30, 30′. These components along with the othercomponents of the second plate 16 are described below.

The microvalve device 10 may have gaps (not shown) between the firstand/or third plates 14, 18 and each of the moving elements of the secondplate 16 including the pilot valve 36, the actuator 38, and the slidervalve 40. These gaps may be formed by thinning the moving elements 36,38, 40 and/or by forming a recess in the first and third plates 14, 18adjacent the moving elements 36, 38, 40. The sizes of the gaps formedbetween the pilot ports 20, 20′, 22, 22′ and the pilot valve 36immediately around the pilot ports 20, 20′, 22, 22′ are small enough toadequately restrict fluid from leaking past the pilot valve 36 when thepilot ports 20, 20′, 22, 22′ are blocked by the pilot valve 36.Preferably, these gaps are approximately 1 micron in size. Similarly,the sizes of the gaps formed between the slider valve 40 and theassociated ports 24, 24′, 26, 26′, 28, 28′, 30, 30′ immediately aroundthe associated ports 24, 24′, 26, 26′, 28, 28′, 30, 30′ are small enoughto adequately restrict fluid from leaking past the slider valve 40 whenthe associated ports 24, 24′, 26, 26′, 28, 28′, 30, 30′ are blocked bythe slider valve 40. Preferably, these gaps also are approximately 1micron in size. The gap sizes of the gaps of all other areas between thefirst and third plates 14, 18 and the moving elements 36, 38, and 40 aresufficiently large enough to provide free movement of the movingelements 36, 38, and 40. Preferably, these gaps are approximately 10microns in size.

The fixed portion 34 defines a cavity 42 and is fixedly attached to thefirst and third plates 14, 16.

The pilot valve 36 is a microvalve formed as an longitudinally elongatebeam having an end flexibly attached to the fixed portion 34 by anelongate flexure beam 36 a. The flexure beam 36 a acts as a hinge formounting the pilot valve 26 in the cavity 42 of the valve body formed bythe first, second, and third plates 14, 16, 18. The flexure beam 36 aforms a reduced-width generally longitudinally extending extension ofthe pilot valve 36. The pilot valve 36 is movably disposed in the cavity42 for pivotal movement between a first position and a second position,the flexure beam 36 a bending as the pilot valve 36 moves. As the pilotvalve 36 pivots, it defines a plane within which the pilot valve 36 ismoving. Preferably, the pilot valve 36 is of a uniform thickness. Withinthe plane of movement of the pilot valve 36, the pilot valve 36 definesa first transverse width. The flexure beam 36 a defines a secondtransverse width that is less than said first transverse width. FIGS. 1Aand 1B show the pilot valve 36 in the first and second positions,respectively. In the first position, the pilot valve 36 blocks orsubstantially closes the second pilot ports 22, 22′ and unblocks orfully opens the first pilot ports 20, 20′. By opening the first pilotports 20, 20′, the pilot valve 36 provides fluid communication betweenthe first pilot ports 20, 20′ and a fluid passage 47 connecting thepilot valve 36 and the slider valve 40. In the second position, thepilot valve 36 unblocks or fully opens the second pilot ports 22, 22′and blocks or substantially closes the first pilot ports 20, 20′. Byopening the second pilot ports 22, 22′, the pilot valve 36 providesfluid communication between the second pilot ports 22, 22′ and the fluidpassage 47. As will be more fully described below, during use the pilotvalve 36 selectively directs “high pressure” fluid into the fluidpassage 47 and selectively vents “high pressure” from the fluid passage47 to operate the placement of the slider valve 40.

The actuator 38 is operably coupled to the pilot valve 36 via aconnecting member 36 b for moving the pilot valve 36 between the firstand second positions. The connecting member 36 b forms an elongateflexure beam defining a third transverse width within the plane ofmovement of the pilot valve 36, the third transverse width being lessthan the first transverse width of the pilot valve 36.

The actuator 38 includes multiple pairs of opposing ribs 44 a and 44 b.Each rib 44 a, 44 b has a first end and a second end. While the ribs 44a and 44 b are shown as being linear and of uniform cross-section alongthe length thereof, it should be understood that the ribs 44 a and 44 bmay be curved, angled, or of non-uniform cross-section if suitable for aparticular application. The first ends of the ribs 44 a and 44 b areattached to the fixed portion 34 adjacent the electrical contacts 32 aand 32 b, respectively. The second ends of the ribs 44 a, 44 b areattached to a spine 46 at respective angles thereto.

Each pair of ribs 44 a and 44 b are generally at an angle to one anotherto form a chevron having an apex at the spine 46. When the electricalcontacts 32 a, 32 b are electrically energized, electrical currentpasses between the electrical contacts 32 a, 32 b through the ribs 44 a,44 b. In turn, the ribs 44 a, 44 b thermally expand. As the ribs 44 a,44 b expand, the ribs 44 a, 44 b elongate, which in turn causes thespine 46 to be displaced. Accordingly, it is preferable that the ribs 44a, 44 b be formed from a conductor or semiconductor material having asuitable thermal expansion coefficient, such as silicon. Additionally,it is preferable that the ribs 44 a, 44 b, the spine 46 and the fixedportion 34 be integrally formed. By regulating the amount of currentsupplied through the ribs 44 a, 44 b, the amount of expansion of theribs 44 a, 44 b can be controlled, thereby controlling the amount ofdisplacement of the spine 46. The combination of the number of ribs 44a, 44 b and the angle formed between the ribs 44 a, 44 b and the spine46 is determinative of the force exerted on the spine 46 and the amountof displacement realized by the spine 46 for a given current supplied.

The connecting member 36 b is fixed to the same longitudinal end of thepilot valve as the flexure beam 36 a, at a point spaced apart from thesupported end of the pilot valve 36 by the flexure beam 36 a. Theconnecting member 36 b extends generally parallel to the flexure beam 36a. However, it will be apparent from inspection of FIGS. 1A and 1B, thatthe connecting member 36 b may be said to be slightly “L-shaped”, whichincreases the offset of the line of force provided by the actuator 38from the hinge provided by the flexure beam 36 a to increase the torqueprovided by the actuator 38 to move the pilot valve 36. Preferably, thepilot valve 36 and the spine 46 are integrally formed. Suitably, theends of the flexure beam 36 a and the connecting member 36 b may beformed with divergent roots therein to minimize stress concentration atthe ends thereof. This is not shown in FIGS. 1A and 1B; however, inFIGS. 5A and 5B (to be discussed below) a flexure beam 136 c hasdivergent roots 136 d and a connecting member 136 e has divergent roots136 f at the ends thereof. A fixed rib 37 extends partially between theconnecting member 36 b and the flexure beam 36 a, the flexure beam 36 b,the rib 37, and the connecting member 36 b cooperating to define a firstslot 37 a. This facilitates fabrication of the slots fixed rib 37defines a fourth transverse width that is substantially the same as thesecond and third widths of the flexure beam 36 a and the connectingmember 36 b. The slot 37 a is defined with a generally “u-shaped”portion when viewed in plan from the perspective looking from the pilotvalve 36 toward the slot 37 a. The slot 37 a is preferably extendedtoward the ribs 44 a of the actuator and communicates with a slot 37 bdefined between one of the ribs 44 a and the adjacent fixed portion 34.This facilitates fabrication of the slot 37 b and the slot 37 a.

When displaced, the spine 46 imparts a force on the pilot valve 36 thatproduces a moment about the supported end of the pilot valve 36. Themoment causes the pilot valve 36 to resiliently bend a first directionabout the supported end of the pilot valve 36, which causes the pilotvalve 36 to move from the first position to the second position. Whenthe electrical contacts 32 a, 32 b are de-energized, the ribs 44 a, 44 bcool and in turn contract. The contraction of the ribs 44 a, 44 b causesthe spine 46 to be displaced in a direction opposite the direction ofthe displacement of the spine 46 due to the expansion of the ribs 44 a,44 b. The displacement of spine 46 due to the contraction of the ribs 44a, 44 b bends the pilot valve 36 in a second direction about thesupported end of the pilot valve 36, which causes the pilot valve 36 tomove from the second position to the first position.

It should be appreciated that the pilot valve 36 may be replaced by anysuitable microvalve capable of opening and closing fluid ports.Additionally, the actuator 38 may be replaced by any actuation meanssuitable for actuating the pilot valve 36 or an appropriate alternativemicrovalve. Indeed, the pilot valve 36 and the actuator 38 need not bemicromachined MEMS devices, although it will normally be advantageousfor these to be so for improved packaging and other considerations. Thedescription regarding the pilot valve 36 and actuator 38 alternativesalso applies to the alternative embodiments of the microvalve devicesdisclosed below.

Referring to FIG. 4, the slider valve 40 is a microvalve formed as agenerally flat T-shaped member having a pair of opposite ends 40 a and40 b and a pair of opposite longitudinally extending sides 40 c and 40d. The slider valve 40 is disposed in the cavity 42 for movement betweena first, fully open position (shown in FIG. 1A) and a second, closedposition (shown in FIG. 1B). It should be appreciated that in certainapplications the slider valve 40 may also be placed in an intermediateor biased position as shown in FIG. 4. The intermediate position of theslider valve 40 is a position between the fully open and closedpositions of the slider valve 40 and is coincident with the “asfabricated” state of the slider valve 40 relative to the fixed portion34. The use of the term “as fabricated” is more clearly defined below.During use, the slider valve 40 assumes the intermediate position whenthe fluid pressure associated with one of the opposing pairs of pilotports 20, 20′, 22, 22′ and the fluid pressures of the primary ports 28,28′, 30, 30′ and the exhaust ports 24, 24′, 26, 26′ are substantiallyequal. An application exemplary of such a condition is discussed below.

The slider valve 40 includes a first portion 48 and a second portion 50interconnected by an intermediate portion 52. Preferably, the first, thesecond and the intermediate portions 48, 50, 52 are integrally formed.When the slider valve 40 is placed in the fully open position, the firstprimary ports 28, 28′ are placed in fluid communication with the secondprimary ports 30, 30′, as shown in FIG. 1A. Accordingly, fluid isallowed to flow between the fluid sources associated with the primaryports 28, 28′, 30, 30′. When the slider valve 40 is placed in the closedposition, the second portion 50 blocks the second primary ports 30, 30′,as shown in FIG. 1B. Having blocked the second primary ports 30, 30′,the slider valve 40 substantially cuts off fluid communication betweenthe first primary ports 28, 28′ and the second primary ports 30, 30′. Asa result, fluid is effectively prevented from flowing between the fluidsources associated with the primary ports 28, 28′, 30, 30′. When theslider valve 40 is placed in the intermediate position, the secondportion 50 unblocks the second primary ports 30, 30′, as shown in FIG.4, thereby allowing fluid flow between the fluid sources associated withthe primary ports 28, 28′, 30, 30′. Additionally, when moving from thefully open position to the closed position, the first portion 48increasingly blocks the exhaust ports 24, 24′, 26, 26′, while the secondportion increasingly blocks the second primary ports 30, 30′. Whenmoving from the closed position to the fully open position, the firstportion 48 increasingly unblocks the exhaust ports 24, 24′, 26, 26′,while the second portion increasingly unblocks the second primary ports30, 30′.

In view of the proximate relationship between the pilot valve 36 and thepilot ports 20, 20′, 22, 22′ and between the slider valve 40 and theprimary ports 28, 28′, 30, 30′, and the exhaust ports 24, 24′, 26, 26′the purpose of having the ports 20, 22, 24, 26, 28, and 30 oppose theports 20′, 22′, 24′, 26′, 28′ and 30′, respectively, can be more clearlyappreciated. Specifically, the pairs of opposing ports provide means ofbalancing fluid forces that act on the upper and lower surfaces of pilotvalve 36 and the slider valve 40. By balancing these forces, neither thepilot valve 36 nor the slider valve 40 are urged by these fluid forcesto contact the first plate 14 or the third plate 18, which wouldotherwise interfere with the movement of the valves 36, 40.

Referring to FIG. 4, the first portion 48 of the slider valve 40includes a first face 54 and a second face 56 opposite the first face54. The second portion 50 of the slider valve 40 includes a first face58 and a second face 60 opposite the first face 58. The first face 54 ofthe first portion 48 is the end 40 a of the slider valve 40 and fluidlycommunicates with the pilot ports 20, 20′, 22, 22′ via the passage 47.The second face 60 of the second portion 50 is the end 40 b opposite theend 40 a. The second face 56 of the first portion 48 and the first face58 of the second portion 50 oppose each other. Preferably, theintermediate portion 52 divides the second face 56 of the first portion48 and the first face 58 of the second portion 50 into substantiallyequal transverse portions. The slider valve 40 is generally of uniformthickness. As such, a comparison of the surface areas of the variousfaces 54, 56, 58, 60 of the slider valve 40 may be made by a comparisonof the length of the various faces 54, 56, 58, 60. It should beappreciated that while the first face 54 and the second face 56 of thefirst portion 48 are shown to have surface areas greater than thesurface areas of the first face 58 and the second face 60 of the secondportion 50, respectively, the surface areas of the first face 54 andsecond face 56 of the first portion 48 may be equal or less than surfaceareas of the first face 58 and the second face 60 of the second portion50, respectively.

First pads or inner pads 62 a and 62 b extend from the second face 56 ofthe first portion 48. One of each of the inner pads 62 a, 62 b isdirectly adjacent one of each of the sides of the intermediate portion52. Second pads or outer pads 64 a and 64 b also extend from the secondface 56 of the first portion 48. The outer pads 64 a and 64 b are spacedapart from the inner pads 62 a, 62 b, respectively, in an outwardtraverse direction. Preferably, the pads 62 a, 62 b, 64 a, 64 b and thefirst portion 48 are integrally formed. The purposes of the pads 62 a,62 b, 64 a, 64 b are discussed below.

A pocket 66 a is defined between the inner and outer pads 62 a, 64 a.The pocket 66 a slightly overlaps the first exhaust ports 24, 24′ whenthe slider valve 40 is in the closed position. As such, the pocket 66 amaintains constant fluid communication with the first exhaust ports 24,24′. The inner pad 62 b and the outer pad 64 b likewise form a pocket 66b between the inner and outer pads 62 b, 64 b. The pocket 66 b and thesecond exhaust ports 26, 26′ are arranged in a manner that places thepocket 66 b in constant fluid communication with the second exhaustports 26, 26′. The purpose of maintaining fluid communication betweenthe pockets 66 a, 66 b and the associated exhaust ports 24, 24′, 26, 26′is discussed below.

A step 68 a is formed in the side 40 c of the first portion 48.Similarly, a step 68 b is formed in the side 40 d of the first portion48. The steps 68 a, 68 b divide the first portion 48 into wide andnarrow portions. The wide portion is adjacent the first face 54 and thenarrow portion is adjacent the second face 56. The purpose of the steps68 a, 68 b is discussed below.

The second portion 50 includes third pads 70 a and 70 b that extend fromthe first face 58. Each of the third pads 70 a, 70 b is directlyadjacent a respective one of the sides 40 c, 40 d of the second portion50. Preferably, the pads 70 a, 70 b and the second portion 50 areintegrally formed. The purpose of the pads 70 a, 70 b is discussedbelow.

The second plate 16 also includes a spring 72 interconnecting the slidervalve 40 and the fixed portion 34. The spring 72 biases the slider valve40 toward the intermediate position (shown in FIG. 4). Additionally, thespring 72 may function as an assembly aid. Specifically, the spring 72may provide a means of holding the slider valve 40 to the fixed portion34 while the second plate 16 is being bonded to the first and/or thirdplates 14, 18. The spring 72 is preferably connected between the firstface 54 of the first portion 48 and a portion of the fixed portion 34opposing the first face 54. Alternatively, the spring 72 may beconnected between the slider valve 40 and the fixed portion 34 in anydesirable arrangement, such as between the second face 60 of the secondportion 50 and a portion of the fixed portion 34 opposing the secondface 60. The spring 72 is shown formed as tension spring but may beformed as a compression spring. Preferably, the spring 72, the slidervalve 40 and the fixed portion 34 are integrally formed. When the spring72, the slider valve 40, and the fixed portion 34 are integrally formed,the spring 72 is in a relaxed state in the intermediate, biased or “asfabricated” position, as shown in FIG. 4. Accordingly, when displacedfrom the intermediate position, the spring 72 biases or urges the slidervalve to return to the intermediate position (shown in FIG. 4).Alternatively, if the spring 72 is separately formed from the slidervalve and/or the fixed portion, the spring 72 may be used to bias theslider valve 40 in the fully open position (shown in FIG. 1A), theclosed position (shown in FIG. 1B) or any position between the fullyopen and closed positions. In applications where the spring 72 is usedsolely as an assembly aid, the spring 72 may be replaced be anon-spring-like member or detachable tether (not shown) connectedbetween the slider valve 40 and the fixed portion 34. Preferably, thetether includes a notch or other suitable pre-stressed feature, whichcauses the tether to breakaway from the slider valve 40 or the fixedportion 34 in a predetermined manner after attaching the second plate 16to the first and third plates 14, 18.

The second plate 16 further includes a sleeve 74 attached to the fixedportion 34 and surrounding at least a portion of the perimeter of theslider valve 40. Preferably, the sleeve 74 and the fixed portion 34 areintegrally formed. When the slider valve 40 is in the intermediateposition (shown in FIG. 4), a generally uniform passage 75 a is definedbetween the sleeve 74 and the side 40 c. Similarly, when the slidervalve 40 is in the intermediate position, a generally uniform passage 75b is defined between the sleeve 74 and the side 40 d. The passages 75 aand 75 b allow free movement of the slider valve 40 between the fullyopen and closed positions by providing clearance between the slidervalve 40 and the sleeve 74. In providing a clearance between the slidervalve 40 and the sleeve 74, the passages 75 permit fluid communicationbetween the ends 40 a and 40 b when the slider valve 40 moves from thefully open position toward the closed position and when the slider valve40 moves from the closed position toward the fully open position betweenthe fully open and closed position. It should be appreciated that incertain applications that fluid flow through the passages may beundesirable if the fluid flow through the passages 75 a, 75 b exceeds aspecified flow rate. Regarding these types of applications, it ispreferable that the passages 75 a, 75 b are sized are small enough toadequately restrict fluid flow between the pilot ports 20, 20′, 22, 22′and the associated exhaust ports 24, 24′, 26, 26′, and between theprimary ports 28, 28′, 30, 30′ and the associated exhaust ports 24, 24′,26, 26′. Generally, it is desirable that the effective restrictions ofthe passage 75 a, 75 b between the end 40 a and the exhaust ports 24,24′, 26, 26′ be greater than the effective restriction of the exhaustports 24, 24′, 26, 26′. Similarly, it is desirable that the effectiverestrictions of the passage 75 a, 75 b between the end 40 b and theexhaust ports 24, 24′, 26, 26′ be greater than the effective restrictionof the exhaust ports 24, 24′, 26, 26′. In other words, it is generallypreferable that flow of fluid through the passages 75 a, 75 b to theexhaust ports 24, 24′, 26, 26′ is restricted more than the flow of fluidthrough the exhaust ports 24, 24′, 26, 26′.

The sleeve 74 includes a pair of steps 79 a and 79 b adjacent the steps68 a and 68 b of the slider valve 40, respectively. The steps 79 a, 79 boccur between a relatively wide portion of the cavity 42 and arelatively narrow portion of the cavity 42. The wide portion of thefirst portion 48 of the slider valve 40 is disposed within the wideportion of the cavity 42 when the slider valve 40 is in the fully openposition (shown in FIG. 1A) and the intermediate position (shown in FIG.4). The wide portion of the first portion 48 of the slider valve 40 isdisposed within the narrow portion of the cavity 42 when the slidervalve 40 is in the closed position (shown in FIG. 1B). The steps 79 a,79 b of the sleeve 74 and the steps 68 a, 68 b of the first portion 48of the slider valve 40 cooperate to reduce the clearance between thesides of the first portion 48 and the sleeve 74 when the slider valve 40moves from the fully open and intermediate positions to the closedposition. By reducing the clearance between the sides of the firstportion 48 and the sleeve 74, fluid flow between the pilot ports 20,20′, 22, 22′ and the exhaust ports 24, 24′, 26, 26′ through the passages75 a, 75 b is greatly restricted. The steps 79 a, 79 b of the sleeve 74and the steps 68 a, 68 b of the first portion 48 of the slider valve 40are preferably slightly inclined relative to the longitudinal axis ofthe slider valve 40. This inclined step arrangement facilitatesalignment and entry of the wide portion of the first portion 48 into thenarrow portion of the cavity 42 as the slider valve 40 moves toward theclosed position from the fully open and intermediate positions.

It should be appreciated that the steps 68 a, 68 b, 79 a, 79 b aredesirable to effectively reduce the clearance between the sides 40 c, 40d of the first portion 48 of the slider valve 40 that would otherwise beminimally achievable by known silicon chip etching techniques.

The sleeve 74 further has opposing seats 76 a and 76 b for limiting themovement of the slider valve 40. The seat 76 a extends from the sleeve74 between the first portion 48 and the second portion 50 of the slidervalve 40 and toward the side 40 c. Similarly, the seat 76 b extends fromthe sleeve 74 between the first portion 48 and the second portion 50 ofthe slider valve 40 and toward the side 40 d. The seats 76 a and 76 bhave first faces 78 a and 78 b, respectively, and second faces 80 a and80 b, respectively. When the slider valve 40 is placed in the closedposition, each inner pad 62 a, 62 b and each outer pad 64 a, 64 b engagethe first face 78 a, 78 b of the associated seat 76 a, 76 b. By engagingthe seats 76 a, 76 b, the inner and outer pads 62 a, 62 b, 64 a, 64 bprevent the slider valve 40 from moving beyond the closed position whenmoving from the intermediate and the fully open positions. Additionally,engagement between the seats 76 a, 76 b and the inner pads 62 a, 62 bfurther restricts fluid flow between the first primary ports 28, 28′ andthe exhaust ports 24, 24′, 26, 26′ through the passages 75 a, 75 b.Furthermore, engagement between the seats 76 a, 76 b and the outer pads64 a, 64 b provides an additional restriction to fluid flow between thepilot ports 20, 20′, 22, 22′ and the exhaust ports 24, 24′, 26, 26′through the passages 75 a, 75 b.

Each third pad 70 a, 70 b engages the associated second face 80 a, 80 bwhen the slider valve 40 is placed in the fully open position. Byengaging the seats 76 a, 76 b, the third pads 70 a, 70 b prevent theslider valve 40 from moving beyond the fully open position when movingfrom the intermediate and closed positions. In addition, engagementbetween the seats 76 a, 76 b and the third pads 70 a, 70 b furtherrestricts fluid flow between the primary ports 28, 28′, 30, 30′ and theexhaust ports 24, 24′, 26, 26′ through the passages 75 a, 75 b.

It should be appreciated that the function of restricting fluid flow asprovided by a given pair of pads 62 a and 62 b, 64 a and 64 b, and 70 aand 70 b is still provided for, though possibly less effectively, shouldthe given pair of pads 62 a and 62 b, 64 a and 64 b, or 70 a and 70 b beomitted.

The placement of the slider valve 40 is determined in part by thedirection of the net force of the fluid forces acting on the faces 54,56, 58, 60 of the slider valve 40. In other words, if the sum of thefluid forces acting on the first face 54 of the first portion 48 and thefirst face 58 of the second portion 50 is less than the sum of the fluidforces acting on the second face 58 of the first portion 48 and thesecond face 60 of the second portion 50, then the net effect of thefluid forces acting on the slider valve 40 will be to urge the slidervalve 40 toward the fully open position. Conversely, if the sum of thefluid forces acting on the first faces 54, 58 is greater than the sum ofthe fluid forces acting on the second faces 56, 60, then the net effectof the fluid forces acting on the slider valve 40 will be to urge theslider valve 40 toward the closed position. Additionally, when the sumof the forces acting on the first faces 54, 58 is substantially equal tothe sum of the forces acting on the second faces 56, 60, the fluidforces acting on the faces 54, 56, 58, 60 have no effect in displacingthe slider valve 40.

Another factor in determining the placement of the slide valve 40 is theforce of the spring 72 acting on the slider valve 40. In applicationspresenting the condition of having the sum of the forces acting on thefirst faces 54, 58 equal the sum of the forces acting on the secondfaces 56, 60, the spring 72 biases the slider valve 40 in theintermediate position. In other applications in which the net effect ofthe fluid forces of the faces 54, 56, 58, 60 is significantly greaterthan the force of the spring 72, the force of the spring 72 may beconsidered negligible.

The fluid force acting on a given face 54, 56, 58, 60 is a function ofthe surface area of and the fluid pressure acting on the given face 54,56, 58, 60. The fluid pressure acting on the given face 54, 56, 58, 60is dependent on many factors including the fluid pressures of theassociated fluid sources; the size of the associated ports 20, 20′, 22,22′, 24, 24′, 26, 26′, 28, 28′, 30, 30′; the effective restriction ofthe flow path between the fluid sources and the associated ports 20,20′, 22, 22′, 24, 24′, 26, 26′, 28, 28′, 30, 30′; the effectiverestriction of the flow path between the ports 20, 20′, 22, 22′, 24,24′, 26, 26′, 28, 28′, 30, 30′ and the given face 54, 56, 58, 60; thefluid viscosity; and other known factors.

The factors affecting the forces acting on the faces 54, 56, 58, 60 arepredetermined such that the position of the pilot valve 36 and theresultant pressurization or depressurization of the passage 47 controlsthe placement of the slider valve 40.

The microvalve device 10 may be configured as a normally open valve oras a normally closed valve. As a normally open valve, the slider valve40 moves toward the closed position when the actuator 38 is energizedand opens when the actuator 38 is de-energized. As a normally closedvalve, the slider valve 40 opens when the actuator is energized andcloses when the actuator 38 is de-energized. Whether the microvalvedevice 10 is configured as a normally open valve or a normally closedvalve depends on the fluid pressures of the fluid sources associatedwith each port 20, 20′, 22, 22′, 24, 24′, 26, 26′, 28, 30, 30′, and thespring force of the spring 72. The microvalve device 10 is configured asa normally open valve, as shown in FIG. 1A, by preferably connecting thefirst pilot ports 20, 20′ to a “low pressure” fluid source and byconnecting the second pilot ports 22, 22′ to a “high pressure” fluidsource. Additionally, as a normally open valve, it is preferable thatthe fluid source associated with the first pilot ports 20, 20′ has afluid pressure no greater than the fluid pressures of the fluid sourcesassociated with the first primary ports 28, 28′ and the exhaust ports24, 24′, 26, 26′, the fluid sources associated with the first primaryports 28, 28′ and the exhaust ports 24, 24′, 26, 26′ have fluidpressures no greater than the fluid pressure of the fluid sourceassociated with the second pilot ports 22, 22′, and the fluid sourceassociated with the second primary ports 30, 30′ has a fluid pressure nogreater than the fluid pressure of the fluid source associated with thefirst primary ports 28, 28′. On the other hand, the microvalve device 10is configured as a normally closed valve (not shown) by preferablyconnecting the first pilot ports 20, 20′ to a “high pressure” fluidsource and by connecting the second pilot ports 22, 22′ to a “lowpressure” fluid source. In addition, as a normally closed valve, it ispreferable that the fluid sources associated with the first primaryports 28, 28′ and the exhaust ports 24, 24′, 26, 26′ have fluidpressures no greater than the fluid pressures of the fluid sourceassociated with the first pilot ports 20, 20′, the fluid sourcesassociated with the second pilot ports 22, 22′ has a fluid pressures nogreater than the fluid pressures of the fluid sources associated withthe first primary ports 28, 28′ and the exhaust ports 24, 24′, 26, 26′,and the fluid source associated with the second primary ports 30, 30′has a fluid pressure no greater than the fluid pressure of the fluidsource associated with the first primary ports 28, 28′.

The microvalve device 10 is made using suitable MEMS fabricationtechniques, such as the fabrication techniques disclosed in U.S. patentapplication Ser. No. 09/148,026 filed Sep. 3, 1998, now abandoned, thedisclosures of which are incorporated herein by reference.

It should be appreciated that the body 12 may be formed from adjoiningplates numbering more or less than three. Regarding these alternativeembodiments, the cavity 42 is defined by a cavity or recess formed inone or more of the adjoining plates.

It should also be appreciated that while it is preferable that thecomponents of the second plate 16 are integrally formed, any or all ofthe components of the second plate 16 may be separately formed andbonded or otherwise suitably attached to the associated component orcomponents.

In operation, when the microvalve 10 is configured as a normally openvalve, the slider valve 40 moves from either the fully open position orthe intermediate position to the closed position when the actuator 38 isenergized. Additionally, when configured as a normally open valve, theslider valve 40 moves from the closed position to either the fully openposition or the intermediate position when the actuator 38 isde-energized. Specifically, when the actuator 38 is energized,electrical current flows through the ribs 44 a, 44 b. The flow ofelectrical current through the ribs 44 a, 44 b causes the ribs 44 a, 44b to thermally expand and elongate. The elongation of the ribs 44 a, 44b in turn displaces the spine 46 from the position shown in FIG. 1A tothe position shown in FIG. 1B.

The displacement of spine 46 then causes the pilot valve 36 to move fromthe first position to the second position thereof, as shown in FIGS. 1Aand 1B, respectively. In moving from the first position to the secondposition, the pilot valve 36 increasingly blocks the first pilot ports20, 20′, while at the same time, the pilot valve 36 increasinglyunblocks the second pilot ports 22, 22′, thereby increasing the pressureof the fluid in the passage 47. In the second position, the“high-pressure” fluid source associated with the second pilot ports 22,22′ is placed in fluid communication with the first face 54 of the firstportion 48 via the passage 47. As a result, the net force of the forcesacting on the faces 54, 56; 58, 60 forces to slider valve 40 to movefrom either the fully open or intermediate positions to the closedposition.

As the slider valve 40 moves toward the closed position, the stepped-upportion of the first portion 48 of the slider valve 40 overlaps thestepped down portion of the sleeve 74, which cause the clearancesbetween the first portion 48 and the sleeve 74 to decrease. Bydecreasing the clearances between the first portion 48 and the sleeve74, the “high-pressure” fluid acting on the first face 54 is furtherrestricted from flowing through the passages 75 a, 75 b to the“low-pressure” fluid source associated with the exhaust ports 24, 24′,26, 26′. Also, as the slider valve 40 moves toward the closed position,the second portion 50 of the slider valve 40 increasingly blocks thesecond primary ports 30, 30′.

Having reached the closed position, the inner and outer pads 62 a, 62 b,64 a, 64 b engage the first faces 78 a, 78 b of the corresponding seats76 a, 76 b, thereby limiting the advancement of the slider valve 40.Additionally, engagement between the outer pad 64 a and the seat 76 arestricts the “high-pressure” fluid acting on the first face 54 of theslider valve 40 from flowing to the “low-pressure” fluid source viapassage 75 a and the first exhaust ports 24, 24′. Similarly, engagementbetween the outer pad 64 b and the seat 76 b restricts the“high-pressure” fluid acting on the first face 54 of the slider valve 40from flowing to the “low-pressure” fluid source via the passage 75 b andthe second exhaust ports 26, 26′. Furthermore, engagement between theinner pad 62 a and the seat 76 a restricts fluid flow from the“high-pressure” fluid source through the first primary ports 28, 28′ tothe “low-pressure” fluid source via the passage 75 a and the firstexhaust ports 24, 24′. Similarly, engagement between the inner pad 62 band the seat 76 b restricts fluid flow from the “high-pressure” fluidsource through the first primary ports 28, 28′ to the “low-pressure”fluid source via the passage 75 b and the second exhaust ports 26, 26′.Finally, when placed in the closed position, the second portion 50 ofthe slider valve 40 fully covers the second primary ports 30, 30′. Bycovering the second primary ports 30, 30′, the slider valve 40effectively blocks fluid from flowing from the “high-pressure” fluidsource through the first primary ports 28, 28′ to the “low-pressure”fluid source through the second primary ports 30, 30′.

When the actuator 38 is de-energized, current ceases to flow through theribs 44 a, 44 b, which causes the ribs 44 a, 44 b to cool and in turn tocontract and shorten. The contraction of the ribs 44 a, 44 b forces thespine 46 to be displaced in a manner which causes the pilot valve 36 tomove from the second position to the first position. In moving from thesecond position to the first position, the pilot valve 36 increasinglyblocks the second pilot ports 22, 22′, while at the same time, the pilotvalve 36 increasingly unblocks the first pilot ports 20, 20′, loweringthe pressure of the fluid in the passage 47. When the pilot valve 36reaches the first position, the “low-pressure” fluid source associatedwith the first pilot ports 20, 20′ is placed in fluid communication withthe first face 54 of the first portion 48 via the passage 47, in placeof the “high-pressure” fluid source associated with the second pilotports 22, 22′. As a result, the net force of the forces acting on thefaces 54, 56, 58, 60 forces to slider valve 40 to move from the closedposition to either the fully open position or intermediate position.

As the slider valve 40 moves from the closed position, the secondportion 50 of the slider valve 40 increasingly unblocks the secondprimary ports 30, 30′. As the second primary ports 30, 30′ areunblocked, fluid is increasing allowed to flow from the “high-pressure”fluid source through the first primary ports 28, 28′ to the“low-pressure” fluid source through the second primary ports 30, 30′.

In reaching the fully open position, the third pads 70 a, 70 b engagethe second faces 80 a, 80 b of the corresponding seats 76 a, 76 b,thereby preventing further advancement of the slider valve 40.Additionally, engagement between the third pad 70 a and the seat 76 afurther restricts fluid flow from the “high-pressure” fluid sourcethrough the first primary ports 28, 28′ to the “low-pressure” fluidsource via the passage 75 a and the first exhaust ports 24, 24′. Inaddition, engagement between the third pad 70 b and the seat 76 bfurther restricts fluid flow from the “high-pressure” fluid sourcethrough the first primary ports 28, 28′ to the “low-pressure” fluidsource via the passage 75 b and the second exhaust ports 26, 26′.

The microvalve device 10 configured as a normally closed valve functionssubstantially the same as the microvalve device 10 configured as anormally open valve as discussed above, except that the slider valve 40of a normally closed configuration opens when the actuator 38 isenergized and closes when the actuator 38 is de-energized.

A second embodiment of a microvalve device for controlling fluid flow ina fluid circuit is shown generally at 110 in FIG. 5A. The microvalvedevice 110 is similar in structure and in function to the microvalvedevice 10, as such similar 100's series (centennial) and 10's series(non-centennial) numbers indicate similar features. For example, themicrovalve device 110 has a body 112, which is generally similar instructure and function to the body 12 of the microvalve device 10. Thedrawings of this second and subsequent embodiments employing centennialnumbering schemes designate features, which unless otherwisespecifically described in the figure in which the reference numberappears, may be taken to be generally similar in structure and functionof the corresponding non-centennial numbered part of the microvalvedevice 10 and explained by reference to description thereof with respectto the microvalve device 10.

The primary differences between the microvalve device 110 and themicrovalve device 10 is that the pilot valve 36 and the slider valve 40have been modified in a manner that eliminates the need for the ports20′, 22′, 24′, 26′, 28′, 30′ formed in the third plate 18. Additionally,the spring 72 has been modified in a manner that reduces any influencethat the spring 72 might have in causing the slider valve 40 to movelaterally when moving between the fully open and closed positions.

The body 112 includes a second plate 116 between and attached to a firstplate 114 and a third plate 118, as best shown in FIG. 6.

Referring to FIGS. 5A and 51B, the first plate 114 defines a first pilotport 120 and a second pilot port 122. The first plate 114 also defines afirst exhaust port 124 and a second exhaust port 126. Referring also toFIG. 6, the first plate 114 further defines a first primary port 128 anda second primary port 130. Alternatively, any or all of the ports 120,122, 124, 126, 128, 130 may be formed in the third plate 118.

Referring to FIG. 7, the third plate 118 defines a primary trough 182 a.The primary trough 182 a aligns with the second primary port 130 as bestshown in FIG. 6. The third plate 118 also defines a first exhaust trough182 b and a second exhaust trough 182 c. The first and second exhausttroughs 182 b and 182 c align with the first and second exhaust ports124 and 126, respectively, in a manner similar to alignment as shown inFIG. 6 between the primary trough 182 a and the second primary port 130.In addition, the third plate 118 defines a first pilot trough 182 d anda second pilot trough 182 d. The first and second pilot troughs 182 dand 182 e align with the first and second pilot ports 120 and 122,respectively, in a manner similar to alignment between the primarytrough 182 a and the second primary port 130. Each trough 182 a–eprovides a similar function, which is discussed below.

Referring to FIGS. 5A, 5B, and 6, the second plate 116 defines a cavity142. A “T-shaped” pilot valve 136 is disposed in the cavity 142 formovement between a first position (shown in FIG. 5A) and a secondposition (shown in FIG. 5B). The pilot valve 136 includes an elongatedbeam 136 a attached to a fixed portion 134 of the second plate 116. Ablocking portion 136 b extends from a free end of the beam 136 a.Preferably, the blocking portion 132 b is formed of two portions thatextend from opposite sides of the beam 136 a. Preferably, each portionof the blocking portion 132 b extends 136 a at an angle of approximatelyninety degrees from to the respective side of the beam 136 a.Alternatively, the portions of the blocking portion 132 b may extendfrom the sides of the beam 136 a at any suitable angle. Preferably, theblocking portion 136 b will be substantially the same plane as the beam136 a. The blocking portion 136 b alternately blocks and unblocks thefirst pilot port 120 and the second pilot port 122 when the pilot valve136 moves between the first and second positions. The blocking portion136 b allows for greater separation between the pilot ports 120, 122,which may be desirable in certain applications.

Referring to FIGS. 5A and 5B, the blocking portion 136 b defines a firstpilot duct 184 a, which extends between upper and lower surfaces of thepilot valve 136. The first pilot duct 184 a is in continuous fluidcommunication with the first pilot port 120 and the first pilot trough182 d (shown in FIG. 7). As such, the first pilot duct 184 a maintainsfluid communication between the first pilot port 120 and the first pilottrough 182 d through the pilot valve 136 in whatever position the pilotvalve 136 is placed in. The blocking portion 136 b also defines a secondpilot duct 184 b, which extends between the upper and lower surfaces ofthe pilot valve 136. Similar to the arrangement between the first pilotduct 184 a, the first pilot port 120, and the first pilot trough 182 d,the second pilot duct 184 b is in continuous fluid communication withthe second pilot port 122 and the second pilot trough 182 e (shown inFIG. 7).

The blocking portion 136 b further defines a pair of first pilot vents186 a and a pair of second pilot vents 186 b. Each pilot vent 186 a, 186b extends between the upper and lower surfaces of the pilot valve 136.The first pilot vents 186 a are adjacent to the first pilot duct 184 aand are adjacent opposite edges of the blocking portion 136 b. Thesecond pilot vents 186 b are adjacent the second pilot duct 184 b andare adjacent opposite edges of the blocking portion 136 b. The purposeof the pilot vents 184 a, 186 b is discussed below.

The second plate 116 further includes a slider valve 140 having oppositeends 140 a and 140 b and opposite sides 140 c and 140 d. The slidervalve 140 is disposed in a sleeve 174 for movement between a first,fully open position and a second, closed position. The sleeve 174 ispreferably integrally formed with the fixed portion 134. FIGS. 5A and 5Bshow the slider valve 140 in the fully open and closed positions,respectively. As with the slider valve 40 (see FIG. 4), the slider valve140 may also be placed in an intermediate or biased position, as shownin FIG. 8, which is a position between the fully open and closedpositions.

Referring to FIG. 8, the slider valve 140 includes a first portion 148and a second portion 150 interconnected by an intermediate portion 152.The second portion 150 defines a plurality of primary ducts 188 thatextend between upper and lower surfaces of the slider valve 140. Eachprimary duct 188 is in continuous fluid communication with the secondprimary port 130 and the primary trough 182 a (shown in FIGS. 6 and 7).As such, the primary ducts 188 maintain fluid communication between thesecond primary port 130 and the primary trough 182 a through the slidervalve 136 in whatever position the slider valve 136 is placed.

The first portion 148 defines a first exhaust duct 190 a, which extendsbetween the upper and lower surfaces of the slider valve 140 and isplaced in continuous fluid communication between the first exhaust port124 and the first exhaust trough 182 b (shown in FIG. 7). The firstportion 148 also defines a second exhaust duct 190 b, which extendsbetween the upper and lower surfaces the slider valve 140 and is placedin continuous fluid communication between the second exhaust port 126and the second exhaust trough 182 c (shown in FIG. 7). As such, theexhaust ducts 190 a, 190 b maintain fluid communication between theexhaust ports 124, 126, respectively, and the respective exhaust ducts182 b, 182 c through the slider valve 140 in whatever position theslider valve 140 is placed.

The first portion 148 further defines a plurality of slider vents 192that extend between the upper and lower surfaces the slider valve 140.The slider vents 192 are distributed along the edges of the end 140 aand the sides 140 c, 140 d.

The ducts 184 a, 184 b, 190 a, 190 b, 188 provide a means of balancingthe fluid pressures that act on the respective valves 136, 140 as aresult of fluid flowing to and from the respective ports 120, 122, 124,126, 130. Specifically, each duct 184 a, 184 b, 190 a, 190 b, 188 allowsfluid to flow between the respective port 120, 122, 124, 126, 130 andthe associated trough 182 d, 182 e, 182 b, 182 c, 182 a, respectively,in a sufficiently nonrestrictive manner so that difference between thefluid pressures acting on the upper and lower surface of the respectivevalve 136, 140 in the area of the particular duct 184 a, 184 b, 190 a,190 b, 188 does not cause the respective valve 136, 140 to move towardand contact the first plate 114 or the third plate 118 in a manner thatwould interfere with the intended movement of the valve 136, 140.

Additionally, the ducts 184 a, 184 b, 190 a, 190 b, 188 in combinationwith the associated trough 182 d, 182 e, 182 b, 182 c, 182 a,respectively, allow for an increased fluid flow rate through therespective ports 120, 122, 124, 126, 130 for a given pressuredifferential across the respective ports 120, 122, 124, 126, 130.Specifically, the fluid flow rate through a given port 120, 122, 124,126, 130 for a given pressure differential is a function of the area ofthe given port 120, 122, 124, 126, 130 unblocked by the respective valve136, 140. When the respective valve 136, 140 is in a position in whichthe respective valve 136, 140 partially covers the given port 120, 122,124, 126, 130, the unblocked area of the given port 120, 122, 124, 126,130 is equal to the area of the given port 120, 122, 124, 126, 130uncovered by the respective valve 136, 140 and the area of the givenport 120, 122, 124, 126, 130 in communication with the respectiveduct(s) 184 a, 184 b, 190 a, 190 b, 188. Whereas, in the absence of therespective ducts 184 a, 184 b, 190 a, 190 b, 188 and the associatedtrough 182 d, 182 e, 182 b, 182 c, 182 a, respectively, the unblockedarea of the given port 120, 122, 124, 126, 130 is limited to the areauncovered by the respective valve 136, 140. As such, the respectiveduct(s) 184 a, 184 b, 190 a, 190 b, 188 and the associated trough 182 d,182 e, 182 b, 182 c, 182 a, respectively, increase the unblock area ofthe given port 120, 122, 124, 126, 130 when the respective valve 136,140 is in a position in which the respective valve 136, 140 partiallycovers the respective port 136, 140. Thus, by increasing the unblockedarea of the given port 120, 122, 124, 126, 130 when the respective valve136, 140 partially covers the respective port 136, 140, the flow ratefor a given pressure differential across the given port 120, 122, 124,126, 130 is increased. FIG. 6 illustrates the fluid flow paths throughthe primary port 130, which are similar to the fluid flow paths of theother ports 120, 122, 124, 126 having a respective duct 184 a, 184 b,190 a, 190 b and the associated trough 182 d, 182 e, 182 b, 182 c,respectively. When the slider valve 140 partially covers the primaryport 130 as shown in FIG. 6, fluid is allowed to flow through theprimary port 130 through an uncovered portion of the primary port 130 asrepresented by flow path f1. In addition, the ducts 188 and the trough182 a allow fluid to flow through the primary port 130 through a portionof the primary port 130 in communication with the ducts 188 asrepresented by flow path f2.

It should be appreciated that while the pilot ducts 184 a, 184 b and theexhaust ducts 190 a, 190 b are shown as being circular and the primaryducts 188 are shown as generally rectangular, the ducts 184 a, 184 b,190 a, 190 b, 188 may be any suitable shape. It should also beappreciated that each of the pilot ducts 184 a, 184 b and each of theexhaust ducts 190 a, 190 b may be replaced a plurality of similarlyformed ducts. Additionally, it should be appreciated that primary ducts188 may be fewer or more in number than the four ducts 188 as shown.

The vents 186 a, 186 b, 192 provide a means of balancing the fluidpressures that act on the respective valves 136, 140 as a result offluid leaking past the valves between the first plate 114 and valves136, 140 and as a result of fluid leaking past the valves 136, 140between the third plate 118 and the valves 136, 140. Specifically, eachvent 186 a, 186 b, 192 is designed to intercept the flow of fluid pastthe respective valve 136, 140 between the respective valve 136, 140 andthe first and third plates 114, 188 and to allow the intercepted fluidto flow through the respective valve 136, 140 in a sufficientlynonrestrictive manner so that difference between the fluid pressuresacting on the upper and lower surface of the respective valve 136, 140in the area of the particular vent 186 a, 186 b, 192 does not cause therespective valve 136, 140 to move toward and contact the first plate 114or the third plate 118 in a manner that would interfere with theintended movement of the valve 136, 140.

It should be appreciated that while the vents 186 a, 186 b, 192 areshown as being generally rectangular, the vents 186 a, 186 b, 192 may beany suitable shape. It should also be appreciated that location and thenumber of vents may vary depending on a particular application to whichthe microvalve device 110 is utilized.

Referring to FIGS. 5A and 5B, the second plate 116 further includes anactuator 138 for controlling the movement of the pilot valve 138. Theactuator 138 includes an elongated spine 146 attached to the pilot valve136. The actuator further includes multiple pairs of opposing first ribs144 a and second ribs 144 b. Each first rib 144 a has a first endattached to a first side of the spine 146 and a second end attached tothe fixed portion 134, specifically to a fixed body 134 a to which aplurality of first ribs 144 a are attached. Similar to the first ribs144 a, each second rib 144 b has a first end attached to a second sideof the spine 146 and a second end attached to a fixed body 134 b formedof the fixed portion 134. Similar to the ribs 44 a, 44 b of themicrovalve device 10 described above, the ribs 144 a, 144 b are designedto thermally expand and contract. Electrical contacts 132 a and 132 bare adapted for connection to a source of electrical power to supplyelectrical current flowing through the ribs 144 a and 144 b to thermallyexpand, to elongate, the ribs 144 a and 144 b. Each end of the ribs 144a, 144 b is tapered for reducing the stress acting on the ribs 144 a,144 b caused by the expansion and contraction of the ribs 144 a, 144 b,by allowing the ends to be more flexible. The mid-section of each of theribs 144 a and 144 b is relatively wider than the ends to maintainrigidity and thus prevent buckling under the compressive loads to whichthe ribs 144 a, 144 b are exposed during thermal elongation.

It is useful in many manufacturing processes, such as the deep reactiveion etching process by which the microvalve device 110 may suitably bemanufactured, to maintain uniform widths of gaps between components inclose proximity to one another, such as adjacent ones of the ribs 144 aillustrated in FIG. 5B. The description of how this may be accomplishedthat follows in the next two paragraphs is equally applicable to theribs 144 b of the microvalve device 110, and similar principals maysuitably may be used on other micromachined structures.

Each of the ribs 144 a has a first portion, the mid-section, which isrelatively wide. Adjacent faces of the ribs 144 a have a slot or gap 144c therebetween which has a given, constant width. In a second portion ofthe ribs 144 a, the portion where the ribs attach to the fixed portion134 a, the adjacent faces of the ribs 144 a are spaced apart by adistance which is greater than the width between the adjacent faces atthe first portion, due to the tapering of the ends of the ribs 144 a. Tomaintain uniform width of the gap between the adjacent second portions,extension bodies 144 d are interposed between longitudinally adjacentsecond portions of the ribs 144 a. A second gap (slot) 144 e is definedbetween each of the extension bodies 144 d and an adjacent one of theribs 144 a. The gap 144 e has the same width as the gap 144 c, andmerges with the gap 144 c adjacent the point where the second portion ofthe adjacent rib 144 a reaches its maximum width. A third gap 144 f isdefined between each of the extension bodies 144 d and the rib 144 alongitudinally adjacent to the rib 144 a that is adjacent to the gap 144e. The gap 144 f has the same width as the gaps 144 c and 144 e, andmerges with the gaps 144 c and 144 e adjacent the point where the secondportion of the adjacent rib 144 a reaches its maximum width. It will beappreciated that the shape of the extension bodies 144 d is determinedby the adjacent shape of the ribs 144 a on either side thereof.

In a third portion of the ribs 144 a, the portion where the ribs attachto the spine 146, the adjacent faces of the ribs 144 a are spaced apartby a distance which is greater than the width between the adjacent facesat the first portion, due to the tapering of the ends of the ribs 144 a.To maintain uniform width of the gap between the adjacent secondportions, additional extension bodies 144 d are interposed betweenlongitudinally adjacent third portions of the ribs 144 a. A fourth gap(slot) 144 g is defined between each of the extension bodies 144 d andan adjacent one of the ribs 144 a. The gap 144 g has the same width asthe gap 144 c, and merges with the gap 144 c adjacent the point wherethe third portion of the adjacent rib 144 a reaches its maximum width. Afifth gap 144 h is defined between each of the extension bodies 144 dand the rib 144 a longitudinally adjacent to the rib 144 a that isadjacent to the gap 144 g. The gap 144 h has the same width as the gaps144 c and 144 g, and merges with the gaps 144 c and 144 g adjacent thepoint where the third portion of the adjacent rib 144 a reaches itsmaximum width.

The microvalve device 110 may be subject to considerable differentialpressure between the interior and exterior surfaces thereof. Accordingto the invention, therefore, the design of the microvalve device 110will preferably include one or more pressure-reinforcing membersextending between spaced-apart portions of the wall surfaces of largeinternal chambers. For example, the actuator 138 includes a firstpressure-reinforcing member 191 a interposed between selected first ribs144 a. The first pressure-reinforcing member 191 a has a fixed endattached to the fixed portion and a free end adjacent to the first sideof the spine 146. The first pressure-reinforcing member 191 a also has alower surface attached to the first plate 114 and an upper surfaceattached to the third plate 118. The actuator 138 also includes a secondpressure-reinforcing member 191 b interposed between a selected secondribs 144 b. The second pressure-reinforcing member 191 b has a fixed endattached to the fixed portion and a free end adjacent to the second sideof the spine 146. The first pressure-reinforcing member 191 a also has alower surface attached to the first plate 114 and an upper surfaceattached to the third plate 118. Preferably, the pressure-reinforcingmembers 191 a, 191 b each have a height, which corresponds to thedimension between the lower and upper surfaces of thepressure-reinforcing members 191 a, 191 b that is uniform and slightlygreater than the height of the ribs 144 a. 144 b. Thepressure-reinforcing members 191 a, 191 b reinforce the connectionsbetween the second plate 116 and the first and third plates 114, 118 byreducing the surface areas of the first and second plates 114, 118 thatare continuously unsupported in the immediate vicinity of the ribs 144a, 144 b. Preferably, the pressure-reinforcing members 191 a, 191 b, theribs 144 a, 144 b, the spine 146 and the fixed portion 134 areintegrally formed. It should be appreciated that it may be desirable,depending on a particular application, to include additionalpressure-reinforcing members 191 a and 191 b interposed betweenadditionally selected ribs 144 a and 144 b, respectively, to therebyreduce the distance between pressure-reinforcing members of themicrovalve device 110.

The pressure-reinforcing members 191 a and 191 b are shown in FIGS. 5Aand 5B in the form of respective pressure-reinforcing “peninsulas”extending from the fixed bodies 134 a, 134 b formed of the fixed portion134. FIGS. 5C and 5D illustrate alternate embodiments ofpressure-reinforcing members. In FIG. 5C, instead of peninsulas,pressure-reinforcing members 191 a′ and 191 b′ disposed between the ribsof the actuator 138 take the form of pressure-reinforcing posts notconnected to the fixed portion 134. The pressure-reinforcing members 191a′ and 191 b′ are interposed between selected ones of the ribs 144 a and144 b. FIG. 5D illustrates an alternate embodiment of the actuator 38.Longitudinally elongate openings 191 c are formed through the spine 46.Pressure-reinforcing posts 191 d are fixed to the first plate 14 and thethird plate 18, and extend through the openings 191 c. The openings 191c are preferably sufficiently longitudinally elongate that neitherlongitudinal end of any opening 191 c will impact thepressure-reinforcing post 191 d extending therethrough throughout therange of motion of the spine 46.

Referring again to FIG. 8, a pair of steps 168 a and 168 a′ are formedin the side 140 c of the first portion 148. Similarly, a pair of steps168 b and 168 b′ are formed in the side 140 d of the first portion 148.The steps 168 a, 168 a′, 168 b, 168 b′ divide the first portion 148 intoa first wide portion 148 a, a second wide portion 148 b and a narrowportion 148 c between the first and second wide portions 148 a and 148b.

The sleeve 174 defines steps 180 a and 180 a′ adjacent and complementaryto the steps 168 a and 168 a′, respectively. Similarly, the sleeve 174defines steps 180 b and 180 b′ adjacent and complementary to the steps168 b and 168 b′, respectively. The steps 180 a, 180 a′, 180 b, 180 b′of the sleeve 174 divide the sleeve 174 into a first wide portion 174 a,a second wide portion 174 b and a narrow portion 174 c between the firstand second wide portions 174 a, 174 b. When the slider valve 140 is inthe intermediate position (as shown in FIG. 8), the narrow portion 148 cof the slider valve 40 is disposed within the narrow portion 174 c ofthe sleeve 174, the first wide portion 148 a of the slider valve 40 isdisposed within the first wide portion 174 a of the sleeve 174, and thesecond wide portion 148 b of the slider valve 40 is disposed within thesecond wide portion 174 b of the sleeve 174. In the intermediateposition, a uniform clearance or passage 175 a is formed between theside 140 c and the sleeve 174. Similarly, in the intermediate position,a uniform clearance or passage 175 b is formed between the side 140 dand the sleeve 174. When the slider valve 140 moves to the fully openposition shown in FIG. 5A, the second wide portion 148 b of the slidervalve 140 is partially disposed in the narrow portion 174 c of thesleeve 174. When the slider valve 140 moves to the closed position shownin FIG. 5B, the first wide portion 148 a of the slider valve 140 ispartially disposed in the narrow portion 174 c of the sleeve 174. Thesteps 180 a, 180 a′, 180 b, 180 b′ of the sleeve 174 and the steps 168a, 168 a′, 168 b, 168 b′ of the slider valve 40 cooperate to greatlyrestrict the flow of fluid through the passages 175 a, 175 b by reducingthe clearances between the first portion 148 and the sleeve 74 when theslider valve 40 moves toward either the closed or fully open positionfrom the intermediate position shown in FIG. 8.

Referring to FIGS. 5A, 5B and 8, the second plate 116 also includes aspring 172 interconnecting the end 140 a of the slider valve 140 and thefixed portion 134. The spring 172 biasing the slider valve 140 in theintermediate position shown in FIG. 8. The spring 172 includes a firstelongated arm 172 a extending from the fixed portion 134. Though shownhaving uniform width, the first arm 172 a will preferably have a reducedwidth “waist” to give a general hour glass shape in plan view. A shim172 b extends from the first arm 172 a toward the slider valve 140. Aright angle is formed between the first arm 172 a and the shim 172 bwhen the spring 172 is in a relaxed state or “as fabricated” position,as shown in FIG. 8. Preferably, the shim 172 a is of generally uniformwidth and thickness. A second elongated aim 172 c extends from the shim172 b toward the end of the first aim 172 a attached to the fixedportion 134. A right angle is formed between the second arm 172 c andthe shim 172 b when the spring 172 is in the “as fabricated” position.Additionally, when the spring 172 is in the “as fabricated” position, agap is formed between the first arm 172 a and the second arm 172 c.Preferably, the second arm 172 c is of generally uniform width andthickness. A third elongated arm 172 d interconnects the second arm 172c and the end 140 a of the slider valve 140. Right angles are formedbetween the third arm 172 d and the second arm 172 c and between thethird arm 172 d and the end 140 a when the spring 172 is in the “asfabricated” position. Preferably, the third arm 172 d is of generallyuniform width and thickness. The shim 172 b is relatively rigid comparedto the first and second arms 172 a, 172 c. The lengths and widths of thefirst arm 172 a and the second arm 172 c are sized so that the first arm172 a and the second arm 172 c bend in a manner which causes the thirdarm 172 d and consequently the slider valve 140 to move along thelongitudinal axis of the slider valve 140 when the slider valve 140moves between the fully open and closed positions. In other words, thefirst arm 172 a and the second arm 172 c are sized so that the third arm172 c maintains a substantially perpendicular relationship to the end140 a of the slider valve 140 when the slider valve 140 moves betweenthe fully open and closed positions.

In manners similar to those described relating to the microvalve device10, the microvalve device 110 may be configured as a normally open valveor as a normally closed valve.

A third embodiment of a microvalve device for controlling fluid flow ina fluid circuit is shown generally at 210 in FIG. 9A. The microvalvedevice 210 is similar in structure and in function to the microvalvedevices 10 and 110, as such similar 200 series, 100 series and 10 seriesnumbers indicate similar features. A primary difference between themicrovalve device 210 and the microvalve device 10 is that the slidervalve 40 of the microvalve device 10 has been modified. As a result ofmodifying the slider valve 40, the orientations of the primary ports 28,30 have also been modified. Additionally, the ports 20′, 22′, 24′, 26′,28′, 30′ formed in the third plate 18 have been eliminated.

The microvalve device 210 includes a body 212. The body 112 includes asecond plate 216 attached between a first plate 214 and a third plate218.

The first plate 214 defines a first primary port 228 and a secondprimary port 230. The first plate 214 also defines a pair of channels294. Alternatively, any or all of the primary ports 228, 230 and thechannels 294 may be formed in the third plate 218. The purpose for thechannels 294 is discussed below.

The second plate 216 includes a slider valve 240 having opposite ends240 a and 240 b and opposite sides 240 c and 240 d. The slider valve 240is disposed in a sleeve 274 for movement between a first, fully openposition and a second, closed position. FIGS. 9A and 9B show the slidervalve 140 in the fully open and closed positions, respectively. As withthe slider valve 40 (see FIG. 4), the slider valve 240 may also beplaced in an intermediate or biased position.

FIG. 10 is an enlargement of the slider valve 240 shown in FIG. 9A. Theslider valve 240 is disposed in a sleeve 272 that is preferablyintegrally formed with a fixed portion 234 of the microvalve device 210.The slider valve 240 includes a first portion 248 and a second portion250 interconnected by an intermediate portion 252. The first portion 248has a first face 254 and a second face 256 opposite the first face 254.The second portion 250 has a first face 258 and a second face 260opposite the first face 258. The first face 254 of the first portion 248and the second face 260 of the second portion 250 are at the ends 240 aand 240 b of the slider valve 240, respectively. The second face 256 ofthe first portion 248 and the first face 258 of the second portion 250oppose each other. The intermediate portion 252 defines a centrallydisposed aperture 296 therethrough.

The slider valve 240 is aligned with the first primary port 228 suchthat the second portion 250 covers a constant area of the first primaryport 228 when moving between the fully open and closed positions.Additionally, when moving between the fully open and closed positions, avarying portion of the first primary port 228 is placed in constantfluid communication with the second face 260 of the second portion 250and another varying portion of the first primary port 228 is placed inconstant fluid communication with the aperture 296. When the slidervalve 240 is in or near the fully open position, the second primary port230 is also placed in fluid communication with the aperture 296. Byplacing both the primary ports 228, 230 in fluid communication with theaperture 296, fluid is allowed to flow between the first primary port228 and the second primary ports 230. When the slider valve 240 is inthe closed position, the second primary port 230 is fully covered by thefirst portion 248. By fully covering the second primary port 230, fluidflow between the first primary port 228 and the second primary port 230is effectively blocked.

The slider valve 240 is aligned with the channels 294 such that one ofeach of the channels 294 is adjacent one of each of the sides 240 c, 240d of the slider valve 140. Each channel 294 places a correspondingportion of the first face 256 of the second portion 250 in constantfluid communication with the aperture 296. The channels 294 are sized sothat the effective restriction to fluid flow through a given channel 294is less than the effective restriction to fluid flow between theinterface of the sleeve 274 and the associated side 240 c, 240 d of theslider valve 240 in the region between the channels 294 and the firstface 256. When the slider valve 240 moves between the fully open andclosed positions, fluid flows through the channels 294 in order toaccommodate for changes in fluid volume between the sleeve 274 and thefirst face 256 of the second portion 250. Alternatively, the channels294 may be formed in the slider valve 240.

In manners similar to those described relating to the microvalve device10, the microvalve device 210 may be configured as a normally open valveor as a normally closed valve.

A fourth embodiment of a microvalve device for controlling fluid flow ina fluid circuit is shown generally at 310 in FIG. 11A. The microvalvedevice 310 is similar in structure and in function to the microvalvedevice 210, as such similar 300 series and 200 series numbers indicatesimilar features. A primary difference between the microvalve device 310and the microvalve device 210 is that the orientations of the primaryports 228, 230 of the microvalve device 210 have been modified. Inaddition, the exhaust ports 224, 226 have been eliminated.

The microvalve device 310 includes a body 312. The body 312 includes asecond plate 316 between and attached to a first plate 314 and a thirdplate 318.

The first plate 314 defines a first primary port 328 and a secondprimary port 330. The first plate 314 also defines a pair of firstchannels 394 a adjacent the first primary port 328 and a pair of secondchannels 394 b adjacent the second primary port 328. Alternatively, theprimary ports 328, 330 and/or the channels 394 a, 394 b may be formed inthe third plate 318.

The second plate 316 includes a slider valve 340 having opposite ends340 a and 340 b and opposite sides 340 c and 340 d. The slider valve 340is movably disposed in a sleeve 374 for movement between a first, closedposition and a second, fully open position. FIGS. 11A and 11B show theslider valve 340 in the closed and fully open positions, respectively.

FIG. 12 is an enlargement of the slider valve 340 as shown in FIG. 11A.The slider valve 340 includes a first portion 348 and a second portion350 interconnected by an intermediate portion 352. The first portion 348has a first face 354 and a second face 356 opposite the first face 354.The second portion 350 has a first face 358 and a second face 360opposite the first face 358. The first face 354 of the first portion 348and the second face 360 of the second portion 350 are at opposites endsof the slider valve 340. The second face 356 of the first portion 348and the first face 358 of the second portion 350 oppose each other. Theintermediate portion 352 defines a centrally disposed aperture 396therethrough.

The slider valve 340 is aligned with the second primary port 330 suchthat the second primary port 330 is placed in constant fluidcommunication with the aperture 396. The slider valve 340 is alignedwith the first primary port 328 such that a varying portion of the firstprimary port 328 is placed in constant fluid communication with thesecond face 360 of the second portion 350. Additionally, when the slidervalve 340 is in the closed position (FIGS. 11A and 12), the secondportion 350 blocks the first primary port 328 except for a portion 328 aof the first primary port 328 that remains in fluid communication withthe second face 360. In doing so, fluid is effectively prevented fromflowing between the primary ports 328, 330. When the slider valve 340moves to the fully open position (FIG. 11B), the second portion 350unblocks an increasing portion of the first primary port 328 adjacentthe first end 358 of the second portion 350. The portion of the firstprimary port 328 unblocked by the second portion 350 is placed in fluidcommunication with the aperture 396. By placing an increasing portion ofthe first primary port 328 in fluid communication with the aperture 396,fluid is increasingly allowed to flow between the primary ports 328,330.

The slider valve 340 is aligned with the first channels 394 a such thatone of the first channels 394 a is in fluid communication with a passage375 a defined by the side 340 c and the sleeve 374. The other firstchannel 394 a is in fluid communication with a passage 375 a defined bythe side 340 d and the sleeve 374. Each first channel 394 a places aportion of the first face 358 in constant fluid communication with theaperture 396. The slider valve 340 is aligned with the second channels394 b such that one the second channels 394 b is in fluid communicationwith the passage 375 a and the other second channel 394 b is in fluidcommunication with a passage 375 b. Each second channel 394 b places aportion of the second face 356 of the first portion 348 in constantfluid communication with the aperture 396. By allowing fluid to flowbetween the passages 375 a and 375 b and the primary port 330 throughthe channels 394 b, the exhaust ports 224, 226 of the microvalve device210 may be eliminated. Each channel 394 a, 394 b is sized so that theeffective restriction to fluid flow through the channel 394 a, 394 b isless than the effective restriction to fluid flow between the sleeve 374and the associated side 340 c, 340 d of the slider valve 340.

In manners similar to those described relating to the microvalve device10, the microvalve device 310 may be configured as a normally open valveor as a normally closed valve.

A fifth embodiment of a microvalve device for controlling fluid flow ina fluid circuit is shown generally at 410 in FIG. 13A. The microvalvedevice 410 is similar in structure and function to the microvalve device310, as such, similar 400 series and 300 series numbers indicate similarfeatures. The primary difference between the microvalve device 410 andthe microvalve device 310 is that slider valve 340 has been convertedfrom a “two-port” valve to a “three-port” valve by adding a thirdprimary port.

The microvalve device 410 includes a body 412. The body 412 includes asecond plate 416 between and attached to a first plate 414 and a thirdplate 418.

The first plate 414 defines a first pilot port 420 and a second pilotport 422. The first plate further defines a first primary port 428, asecond primary port 430 and a third primary port 498. Alternatively, anynumber of the ports 420, 422, 428, 430, 498 may be formed in the thirdplate 418. The first pilot port 420 is adapted for connection with a“low pressure” fluid source (not shown). The second pilot port 422 isadapted for connection with a “high pressure” fluid source (not shown).One of each of the primary ports 428, 430, 498 is adapted for connectionto one of each of three different fluid sources (not shown). The fluidsource associated with the third primary port 498 has a fluid pressurehigher than the fluid pressure of the fluid source associated with thesecond primary port 430. Preferably, the fluid source associated withthe first primary port 428 has a fluid pressure higher than the fluidpressure of the fluid source associated with the second primary port430. Alternatively, the fluid source associated with the first primaryport 428 may have a fluid pressure lower than the fluid pressure of thefluid source associated with the second primary port 430.

Referring to FIGS. 13A and 13B, the second plate 416 includes a fixedportion 434 that defines a cavity 442. A pilot valve 436 extends fromthe fixed portion 434 and is movably disposed in the cavity 442 formovement between a first position (shown in FIG. 13A) and a secondposition (shown in FIG. 13B). In the first position, the pilot valve 436blocks the second pilot port 422, which effectively blocks fluidcommunication between the passage 447 and the high pressure sourceassociated with the second pilot port. Additionally, when in the firstposition, the pilot valve 436 unblocks the first pilot port 420. Whenthe first pilot port 420 is unblocked fluid is allowed to flow betweenthe passage 447 and the low pressure source associated with the firstpilot port 420, which in turn allows the fluid pressure in the passage447 to decrease. When moving to the second position, the pilot valve 436increasingly unblocks the second pilot ports 422 and increasingly blocksthe first pilot ports 420, which causes the fluid pressure in thepassage 447 to increase. In the second position, the pilot valve 446fully opens the second pilot port 420 and substantially closes the firstpilot port 422, which allows the fluid pressure in the passage 447 toapproach the fluid pressure of the high pressure source associated withthe second pilot port 422.

An actuator 438 is operably coupled to the pilot valve 436 for movingthe pilot valve 436 between the first and second positions. The actuator438, like the actuator 38 is formed of at least one pair of ribs 44 aand 44 b arranged in a chevron to actuate a central spine 44.Periodically interposed between pairs of the ribs 444 a and the ribs 44b are pressure-reinforcing members 491 a and 491 b, respectively. Thepressure-reinforcing members 491 a and 491 b are similar in structureand function to the pressure-reinforcing members 191 a and 191 b of themicrovalve device 110, described above.

The actuator 438 may be either controlled in a manner so as to controlthe movement of the pilot valve 436 in a two-positional operation modeor a proportional operation mode. When the pilot valve 436 operates inthe two-positional operation mode, the pilot valve 436 acts as an on-offvalve and is placed in a transient state when moving between the firstand second positions. When the pilot valve 436 operates in theproportional operation mode, the pilot valve 436 may be held in anyposition between the first and second positions.

The second plate 416 further includes a slider valve 440 having oppositeends 440 a and 440 b and opposite sides 440 c and 440 d. The slidervalve 440 is movably disposed in a sleeve 474, which defines a portionof the cavity 442, for movement between a first position (shown in FIG.13A) and a second position (shown in FIG. 13B). As described above, whenthe pilot valve 436 operates in the proportional operation mode, theslider valve 440 may also be placed in any position between the firstand second positions including an intermediate closed position in whichthe port 428 is effectively blocked by the slider valve 440 (not shown).The various positions of the slider valve 440 are further describedbelow.

FIG. 14 is an enlargement of the slider valve 440 illustrated in thefirst position shown in FIG. 13A. The slider valve 440 includes a firstportion 448 and a second portion 450 interconnected by an intermediateportion 452. The intermediate portion 452 defines a centrally locatedaperture 496 therethrough. The first portion 448 is wider than theintermediate portion 452 and has a first face 454 and a second face 456opposite the first face 454. The first face 454 of the first portion 448is at an end 440 a of the slider valve 440. The end 440 a of the slidervalve 440 is placed in fluid communication with the first pilot port 420when the pilot valve 436 is in the first position (as shown in FIG.13A). The end 440 a of the slider valve 440 is placed in fluidcommunication with the second pilot port 422 when the pilot valve 436 isin the second position (as shown in FIG. 13B). The end 440 a of theslider valve 440 is placed in decreasing fluid communication with thefirst pilot port 420 and increasing fluid communication with the secondpilot port 422 when the pilot valve 436 moves from the first position tothe second position. Conversely, the end 440 a of the slider valve 440is placed in increasing fluid communication with the first pilot port420 and decreasing fluid communication with the second pilot port 422when the pilot valve 436 moves from the second position to the firstposition.

The second portion 450 has a squared U-shaped face 460 that defines theend 440 b of the slider valve 440. The second portion 450 includes ablocking portion 450 a extending from the intermediate portion 452. Theblocking portion 450 a is substantially the same width as theintermediate portion 452. A pair of longitudinal extensions 450 b extendfrom the blocking portion 450 a away from the intermediate portion 452.An outer edge of each extension 450 b aligns with a side edge of theblocking portion 450 a so as to extend the length of the gaps definedbetween the inner walls of the sleeve 474 and the respective sides 440 cand 440 d, thus increasing the restrictions presented by the leak pathsthrough these gaps. The extensions 450 b, thus, act to increase the headloss relating to fluid flow between the face 460 of the second portion450 and the second face 456 of the first portion 448 so as to increasethe pressure differential between fluid acting on the faces 460 and 456.It should be appreciated that in certain applications the extensions 450b may be eliminated if an adequate pressure differential can beotherwise maintained.

The slider valve 440 is aligned with the second primary port 430 suchthat the second primary port 430 is placed in constant fluidcommunication with the aperture 496. The slider valve 440 is alignedwith the third primary port 498 such that the third primary port 498 isplaced in constant fluid communication with the face 460 of the secondportion 450. When the slider valve 440 is placed in the intermediateposition, the blocking portion 450 a completely covers and effectivelyblocks the first primary port 428. By completely covering the firstprimary port 428, the slider valve 440 effectively prevents fluid flowbetween any of the primary ports 428, 430, 498. When the slider valve440 moves from the intermediate position to the first position, theblocking portion 450 a unblocks an increasing portion of the firstprimary port 428 adjacent the face 460 of the second portion 450. Byincreasingly unblocking the portion of the first primary port 428adjacent the face 460 of the second portion 450, the slider valve 440places the first primary port 428 in increasing fluid communication withthe third primary port 498 giving rise to increasing flow of fluidtherebetween. When the slider valve 440 moves from the intermediateposition to the second position, the blocking portion 450 a unblocks anincreasing portion of the first primary port 428 adjacent the aperture496. By increasingly unblocking the portion of the first primary port428 adjacent the aperture 496, the slider valve 440 places the firstprimary port 428 in increasing fluid communication with the secondprimary port 430 giving rise to increasing flow of fluid therebetween.

The second plate 416 further includes a tension spring 472interconnecting the fixed portion 434 and the end 440 a of the slidervalve 440.

During use, when the pilot valve 436 is moved to the first position,pressure in the passage 447 is reduced, which in turn reduces thepressure acting on the face 454 of the slider valve. The slider valve440 is then urged to move to the first position, shown in FIG. 13A, bythe relatively high pressure maintained at the third primary port 498.When the pilot valve 436 is moved to the second position, pressure inthe passage 447 is increased, which in turn increases the pressureacting on the face 454 of the slider valve 440. The force of theincreased pressure acting on the relatively large area of the face 454overcomes the force generated by the pressure acting on the relativelysmall area of the face 460 to move the slider valve 440 to the secondposition. In addition, when the pilot valve 436 operates in theproportional operation mode, the slider valve 440 may be moved and heldin a position between the first and second position thereof by balancingof the fluid force acting on the first face 454 with net force of thefluid forces acting on the faces 456 and 460 and the force of the spring472.

In a manner similar to that described relating to the microvalve device10, the microvalve device 410 may be configured as normally positionedin either the first position or the second position.

The microvalve devices 10, 110, 210, 310 and 410 may be used in avariety of fluid control applications including anti-lock brake systemsfor automotive vehicles.

A first embodiment of a brake system for an automotive vehicle brakesystem incorporating a microvalve device of this invention is showngenerally at 500 in FIGS. 15A, 15B and 15C. The brake system 500includes a microvalve unit, indicated generally at 502, connected influid communication with a conventional master cylinder 504 and aconventional wheel brake 506 for controlling fluid flow between themaster cylinder 504 and the wheel brake 506. A conventional pump 508 isconnected in fluid communication with the microvalve unit 502 and themaster cylinder 504 for transferring fluid to and from the wheel brake506.

The brake system 500 as shown is configured to provide an anti-lockbrake system (ABS) function. It is understood that other brake systemsmay include additional components. Such components may be placed indifferent fluid communication arrangements depending on the specifiedperformance requirements and/or functions provided by the designatedbrake system.

The microvalve unit 502 includes the microvalve device 10 configured asa normally open valve for controlling fluid flow between the mastercylinder 504 and the wheel brake 506. The microvalve unit 502 furtherincludes a microvalve device 10′ for controlling fluid flow from thewheel brake 506 to the pump 508. The microvalve device 10′ is identicalto the microvalve device 510, except for being configured as a normallyclosed valve.

It should be appreciated that any one of the microvalve devices 110, 210and 310 configured as a normally open valve may replace the microvalvedevice 10 of the microvalve unit 502. Similarly, any one of themicrovalve devices 110, 210 and 310 configured as a normally closedvalve may replace the microvalve device 10′ of the microvalve unit 502.

The first pilot ports 20, 20′ of the microvalve device 10 and the secondpilot ports 22, 22′ of the microvalve device 10′ are each connected influid communication with the inlet of the pump 508 via a conduit 510.The conduit 510, being connected to the inlet of the pump 508, acts a“low pressure” fluid source.

The second pilot ports 22, 22′ of the microvalve device 10 and the firstpilot ports 20, 20′ of the microvalve device 10′ are each connected influid communication with a conduit 512. The conduit 512 is connected influid communication with the master cylinder 504 and a discharge side oroutlet of the pump 508. As such, during braking events, the conduit 512acts as a “high pressure” fluid source with respect to the first faces54 of the first portions 48 of the slider valves 40 of the microvalvedevices 10, 10′.

The first primary ports 28, 28′ of the microvalve device 10 are alsoconnected to the conduit 512. As such, during braking events, theconduit 512 acts as a “high pressure” fluid source with respect to thesecond face 60 of the second portion 50 of the associated slider valve40. The second primary ports 30, 30′ of the microvalve device 10 areconnected to the wheel brake 506 via a conduit 514. When the slidervalve 40 of the microvalve device 10 is in the fully open position andthe pressure of the fluid in conduit 512 is higher than the pressure ofthe fluid in conduit 514, fluid flows from the master cylinder 504 tothe wheel brake 506. When the slider valve 40 of the microvalve device10 is in the fully open position and the pressure of the fluid inconduit 512 is lower than the pressure of the fluid in conduit 514,fluid flows from the wheel brake 506 to the master cylinder 504. Whenthe slider valve 40 of the microvalve device 10 is in the closedposition, fluid flow between the master cylinder 504 and the wheel brake506 is substantially prevented.

The first primary ports 28, 28′ of the microvalve device 10′ areconnected to the wheel brake 506 via a conduit 516. As such, duringbraking events, the conduit 516 acts as a “high pressure” fluid sourcewith respect to the second face 60 of the second portion 50 of theassociated slider valve 40. The second primary ports 30, 30′ of themicrovalve device 10′ are connected to the inlet of the pump via theconduit 510. When the slider valve 40 of the microvalve device 10′ is inthe open position fluid is allowed to flow from the wheel brake 506 tothe inlet of the pump 508. When the slider valve 40 of the microvalvedevice 10′ is in the closed position, fluid flow from the wheel brake506 to the inlet of the pump 508 is substantially prevented.

Though not schematically represented, the exhaust ports 24, 24′, 26, 26′of both of the microvalve devices 10 and 10′ are connected the inlet ofthe pump 508 via conduit 510. As such, during non-braking events, thepressures of the fluid acting on each of the faces 54, 56, 58, 60 of theslider valve 40 are generally equal. Consequently, during non-brakingevents, slider valve 40 is biased by the spring 72 in the intermediateposition.

The brake system 500 operates in one of three operating modes; includinga normal mode, which is the mode of operation during non-ABS braking(foundation braking) and during ABS “apply mode” braking; a hold mode ofABS operation; and a dump mode of ABS operation.

FIG. 15A shows the brake system 500 in the normal mode. During thenormal mode, the actuator 38 of the microvalve device 10 isde-energized. Accordingly, the associated pilot valve 36 is placed inthe first position. By placing the pilot valve 36 of the microvalvedevice 10 in the first position, the first face 54 of the associatedslider valve 40 is placed in fluid communication with the “low pressure”conduit 510. During braking events, the slider valve 40 of themicrovalve device 10 is urged in the fully open position by the “highpressure” fluid of the conduit 512 acting on the associated second face60. On the other hand, during non-braking events in which the pressureof the fluid in the conduit 512 is substantially equal to the pressureof the fluid in the conduit 510, the slider valve 40 of the microvalvedevice 10 is biased in the intermediate position by the associatedspring 72. Having placed the slider valve 40 of the microvalve device 10in either the fully open or the intermediate positions, fluid is allowedto flow between the master cylinder 504 and the wheel brake 506.

Also during the normal mode, the actuator 38 of the microvalve device10′ is de-energized. Accordingly, the associated pilot valve 36 isplaced in the first position. By placing the pilot valve 36 of themicrovalve device 10′ in the first position, the first face 54 of theassociated slider valve 40 is placed in fluid communication with theconduit 512. During events in which the conduit 512 acts as a “highpressure” fluid source, the slider valve 40 of the microvalve device 10′is urged in the closed position by the “high pressure” fluid acting onthe first face 54 of the slider valve 40 of the microvalve device 10′.Having placed the slider valve 40 of the microvalve device 10′ in theclosed position, fluid is effectively prevented from flowing from thewheel brake 506 to the inlet of the pump 508. On the other hand, duringnon-braking events in which the pressure of the fluid in the conduit 516is substantially equal to the pressure of the fluid in the conduit 510,the slider valve 40 of the microvalve device 10′ is biased in theintermediate position by the associated spring 72.

FIG. 15B shows the brake system 500 in the hold mode of ABS operation.During the hold mode of ABS operation, the actuator 38 of the microvalvedevice 10′ remains de-energized and conduit 512 acts as a “highpressure” fluid source. As described above, when the actuator 38 of themicrovalve device 10′ is de-energized and the conduit 512 acts as a“high pressure” fluid source, the associated slider valve 40 is placedin the closed position. As such, fluid is effectively prevented fromflowing from the wheel brake 506 to the inlet of the pump 508.

Also during the hold mode of ABS operation, the actuator 38 of themicrovalve device 10 is energized and the conduit 512 acts as a “highpressure” fluid source. By energizing the actuator 38 of the microvalvedevice 10, the associated pilot valve 36 is placed in the secondposition. By placing the pilot valve 36 of the microvalve device 10 inthe second position, the first face 54 of the associated slider valve 40is placed in fluid communication with the “high pressure” conduit 512.The “high pressure” fluid of the conduit 512 acting on the first face 54of the associated slider valve 40 then urges the associated slider valve40 to move to the closed position. Having placed the slider valve 40 ofthe microvalve device 10 is in the closed position, fluid is effectivelyprevented from flowing between the conduit 512 and the wheel brake 506.Thus, in the hold mode of ABS operation, the slider valves 40 of boththe microvalve devices 10, 10′ are placed in the closed positions.Having closed the slider valves 40 of both the microvalve device 10,10′, the wheel brake 506 is isolated from the remaining portion of thebrake system 500 such that the fluid pressure of the wheel brake 506 isheld substantially constant.

FIG. 15C shows the brake system 500 in the dump mode of ABS operation.During the dump mode, the actuator 38 of the microvalve device 10 isenergized and the conduit 512 acts as a “high pressure” fluid source. Asdescribed above with respect to the hold mode of ABS operation, when theactuator 38 of the microvalve device 10 is energized and the conduit 512acts as a “high pressure” fluid source, the slider valve 40 of themicrovalve device 10 is placed in the closed position. Having placed theslider valve 40 of the microvalve device 10 in the closed position,fluid is effectively prevented from flowing between the conduit 512 andthe wheel brake 506.

Also during the dump mode of ABS operation, the actuator 38 of themicrovalve device 10′ is energized. In turn, the associated pilot valve36 is placed in the second position. By placing the pilot valve 36 ofthe microvalve device 10′ in the second position, the first face 54 ofthe associated slider valve 40 is placed in fluid communication with the“high pressure” conduit 512. The “high pressure” fluid of the conduit512 in turn urges the slider valve 40 of the microvalve device 10′ tomove to the fully open position. Having placed the slider valve 40 ofthe microvalve device 10′ in the filly open position, fluid is allowedto flow from the wheel brake 506 to the inlet of the pump 508.

A second embodiment of a brake system for an automotive vehicleincorporating this invention is shown generally at 600 in FIGS. 16A and16B. The brake system 600 is similar in structure and in function to thebrake system 500, as such, similar 600 series and 500 series numbersindicate similar features. The brake system 600 includes the microvalvedevice 410 configured as a two-position valve. The microvalve device 410is connected in fluid communication with a conventional master cylinder604 and a conventional wheel brake 606 for controlling fluid flowbetween'the master cylinder 604 and the wheel brake 606. A conventionalpump 608 is connected in fluid communication with the microvalve device410 and the master cylinder 604 for transferring fluid to and from thewheel brake 606.

The brake system 600 as shown is configured to provide an anti-lockbrake system (ABS) function. It is understood that other brake systemsmay include additional components. Such components may be placed indifferent fluid communication arrangements depending on the specifiedperformance requirements and/or functions provided by the designatedbrake system.

The first pilot port 420 is connected in fluid communication with theinlet of the pump 608 via a conduit 610. The conduit 610, beingconnected to the inlet of the pump 608, acts a “low pressure” fluidsource.

The second pilot port 422 is connected in fluid communication with aconduit 612. The conduit 612 is connected in fluid communication withthe master cylinder 604 and a discharge side or outlet of the pump 608.As such, during braking events, the conduit 612 acts as a “highpressure” fluid source with respect to the first face 454 of the firstportion 448 of the slider valve 440.

The third primary port 498 is also connected to the conduit 512. Assuch, during braking events, the conduit 612 acts as a “high pressure”fluid source with respect to the face 460 of the second portion 450 ofthe slider valve 440. The second primary port 430 is connected to thewheel brake 606 via a conduit 614. The first primary port 428 isconnected to the conduit 610.

When the slider valve 440 is in the first position and the pressure ofthe fluid in conduit 612 is higher than the pressure of the fluid inconduit 614, fluid flows from the master cylinder 604 to the wheel brake606. When the slider valve 440 is in the first position and the pressureof the fluid in conduit 612 is lower than the pressure of the fluid inconduit 614, fluid flows from the wheel brake 606 to the master cylinder604. When the slider valve 440 is in the second position, fluid isallowed to flow between the wheel brake 606 and the inlet of the pump608.

The brake system 600 operates in one of two operating modes including anormal mode and a dump mode. The normal mode is an operation mode duringnon-ABS braking (foundation braking) and during ABS “apply mode”braking. The dump mode is an operation mode during ABS operation.

FIG. 16A shows the brake system 600 in the normal mode. During thenormal mode, the actuator 438 is de-energized. Accordingly, theassociated pilot valve 436 is placed in the first position. By placingthe associated pilot valve 436 in the first position, the first face 454of the associated slider valve 440 is placed in fluid communication withthe “low pressure” conduit 510. During braking events, the slider valve440 is urged in the first position by the “high pressure” fluid of theconduit 612 acting on the face 460 of the slider valve 440. On the otherhand, during non-braking events in which the pressure of the fluid inthe conduit 612 is substantially equal to the pressure of the fluid inthe conduit 610, the slider valve 40 is biased in an intermediateposition by the spring 472. Preferably, the intermediate positionrepresents a position nearly identical to the first position. Havingplaced the slider valve 440 in either the fully open or intermediatepositions, fluid is allowed to flow between the master cylinder 604 andthe wheel brake 606.

FIG. 16B shows the brake system 600 in the dump mode of ABS operation.During the dump mode, the actuator 438 is energized and the conduit 612acts as a “high pressure” fluid source. In turn, the pilot valve 436 isplaced in the second position. By placing the pilot valve 436 in thesecond position, the first face 454 of the slider valve 440 is placed influid communication with the “high pressure” conduit 612. The “highpressure” fluid of the conduit 612 acting on the first face 454 of theslider valve 440 in turn urges the slider valve 440 in to the secondposition. Having placed the slider valve 440 in the second position,fluid is allowed to flow from the wheel brake 606 to the inlet of thepump 608.

A third embodiment of a brake system for an automotive vehicleincorporating this invention is shown generally at 700 in FIG. 17. Thebrake system 700 is similar in structure and in function to the brakesystem 600, as such, similar 700 series and 600 series numbers indicatesimilar features. The primary difference between the brake system 700and the brake system 600 is that the microvalve device 410 has beenconfigured as a proportional valve. As such, the actuator may move andhold the pilot valve 436 in positions between the first and secondpositions of the pilot valve 436. The placement of the pilot valve 436in a position between the first and second positions causes the fluidacting on the first face 454 of slider valve 440 to assume a pressurehaving a valve between the pressures of the fluid sources associatedwith the pilot ports 420, 422. In turn, the net force acting on theslider valve 440 forces the slider valve 440 to move to a respectiveposition between the first and second positions of the slider valve 440.Included in the positions between the first and second positions of theslider valve 440 is the intermediate position in which the first primaryport 428 is completely covered by the blocking portion 450 a. When theslider valve 440 is in the intermediate position, the wheel brake 706 isisolated from the remaining portion of the brake system 700 such thatfluid flow to or from the wheel brake 506 is substantially prevented.

In accordance with the provisions of the patent statutes, the principleand mode of operation of this invention have been explained andillustrated in its preferred embodiment. However, it must be understoodthat this invention may be practiced otherwise than as specificallyexplained and illustrated without departing from its spirit or scope.

1. A microvalve comprising: a generally planar plate valve body defininga chamber; and a plate valve member movable in said chamber about apivot axis perpendicular to said valve body to control the flow of afluid through said valve body, said plate valve member defining a pairof opposite faces, a first duct therethrough providing fluidcommunication between said opposite faces to equalize fluid pressuresacting on said opposite faces in the region of said first duct, and asecond duct therethrough providing fluid communication between saidopposite faces to equalize fluid pressures acting on said opposite facesin the region of said second duct, said first duct and said second ductbeing equidistant from said pivot axis.
 2. The microvalve defined inclaim 1, said valve body further defining a first port communicatingwith said chamber which is adapted to be connected to a source of highpressure fluid, and defining a second port communicating with saidchamber which is adapted to be connected to a low pressure reservoir,said plate valve member being movable to a position in which said firstduct is in fluid communication with said first port, and said secondduct is in fluid communication with said second port.
 3. The microvalvedefined in claim 2, wherein said plate valve member is “T-shaped”,comprising a main shaft connected to said pivot and a cross-memberhaving a first end portion defining said first duct, a second endportion defining said second duct, and a middle portion between saidfirst and second end portions fixed to said main shaft.
 4. Amicromachined device, comprising: a body comprising a plurality ofplates defining a plurality of parallel planes, said body defining achamber within at least one intermediate plate and a fluid portcommunicating with said chamber; and a member movable in said chamberwithin a plane parallel to said plurality of parallel planes, saidmember having a first portion and a second portion, said member beingmovable within a fixed range of movement such that only said firstportion of the member is adjacent to said fluid port within said fixedrange of movement, said member defining a pair of opposite faces, andfurther defining a vent through said second portion providing fluidcommunication between said opposite faces of said member to equalizefluid pressures acting on said opposite faces of said member.
 5. Themicromachined device defined in claim 4, wherein said member is a valvemember movable to control the flow of a fluid through said fluid port.6. The micromachined device defined in claim 5, wherein said valvemember is “T-shaped”, comprising a main shaft connected to a pivot and across-member comprising said first portion, and a third portion, saidsecond portion being disposed between said first portion and said thirdportion, said first portion having a first duct defined therethrough,said third portion defining a second duct defined therethrough, saidbody defining a second fluid port in fluid communication with saidchamber, only said third portion of said member being adjacent to saidsecond fluid port within said fixed range of movement.
 7. Themicromachined device defined in claim 6, wherein said member is movable,within said fixed range of motion, to a first position in which saidfirst duct is in unrestricted fluid communication with said fluid portand said second duct is in restricted fluid communication with saidsecond fluid port, and movable to a second position in which said firstduct is in restricted fluid communication with said fluid port and saidsecond duct is in unrestricted fluid communication with said secondfluid port.
 8. The micromachined device defined in claim 6, wherein saidvent is formed through said second portion adjacent said first duct, andfurther including a second vent defined through said second portionadjacent said second duct providing fluid communication between saidopposite faces of said member to equalize fluid pressures acting on saidopposite faces of said member.
 9. The micromachined device defined inclaim 6, wherein said vent is formed through said second portionadjacent said first duct, and further including a second vent definedthrough said second portion adjacent said vent providing fluidcommunication between said opposite faces of said member to equalizefluid pressures acting on said opposite faces of said member.
 10. Themicromachined device defined in claim 6, wherein said vent is formedthrough said second portion adjacent said first duct, and wherein saidvent is one of a pair of laterally spaced apart vents formed throughsaid second portion adjacent said first duct, and further including asecond pair of laterally spaced apart vents defined through said secondportion adjacent said second duct providing fluid communication betweensaid opposite faces of said member to equalize fluid pressures acting onsaid opposite faces of said member.